Aside from participles, there are a number of other common mechanisms for forming adjectives from verbs, but these were not part of formal conjugation and unlike participles could not interact with the system of tenses.
-ima: Probably the best known the verbal adjective suffixes, -ima is used to express possibility, and is roughly equivalent to English “-able, -ible”: cen- “see” → cénima “visible, able to be seen”. Tolkien discussed this suffix in several places, including the Quenya Verbal System (QVS) of the late 1940s, Common Eldarin: Verb Structures (EVS2) of the early 1950s and Late Notes on Verb Structure (LVS) written in 1969:
Adjectives expressing possibility: “able to be done”, like “-able, ible”, are formed with -imā, always in simple verbs preceded by a stem strengthened, either by doubling of the final base medial (usual in case of p, t, k), or by lengthening of base vowel, or by nasal intrusion. Thus: mattima “edible”; qettima “utterable”, alqettima “unutterable”; alkárima “impossible to make”; kénima “visible”; alistima “unknowable, secret”. Verbs in -ā drop this: alfárima “impossible to pursue”. Those in u usually keep it: lī̆ruima “able to be sung”. Weak verbs show ălima [from ´ālimā́]: ortalima “able to be raised”; alaniñkwitálima “that cannot be made white (again)”. So istalima “knowable, ascertainable” (QVS, PE22/110).
imā and other elongated forms expressed possibility: kārimā, kartimā “able to be done, feasible”; matˢtima “edible”. But in intransitive verbs -ima meant much [the] same as as ula [see below], cálima “likely to shine, bright”. (In Q. ima was usually added either to a lengthened stem: kárima; or took the form tima: mastima “edible”) (EVS2, PE22/137)
Ex. of ima. tírima “able to be watched, observable”; kénima “visible”; kárima, ”feasible, possible (to do)”, ankárima “very doable, easy”; mátima “edible”; nótima “countable, limited in number (weight or measure)” ... kólima “bearable, light (of burdens and things comparable, troubles, labour, afflictions)”; púlima “pourable, liquid”; yúlima “drinkable”; túvima “discoverable”; kúvima “concealable”. These adjectives were made chiefly from transitive verbal stems (LVS, PE22/155).
All these documents agree on the essential meaning of -ima, but Tolkien’s ideas for how these adjectives were formed seems to have evolved over time. In QVS, the stem of basic verbs was “strengthened” in some way via either vowel lengthening or doubling the final consonant (mattima). In EVS2 consonant doubling seems to be abandoned, but a variant suffix -tima was sometimes used with basic verb (mat+timā > mastima). In LVS vowel lengthening seems to be the only mechanism for strengthening the stem (mátima).
In QVS u-verbs added the suffix -ima directly to the stem (líruima “singable”) but the final a was replaced in half-strong and a-verbs like istima “knowable” and fárima “pursuable”, with vowel lengthening if possible. In QVS transitive and weak verbs use the suffix -lima (ortalima “raisable”) but in LVS it seems the extra l was abandoned and the result was forms like tultaima “fetchable” (PE22/156).
Mostly -ima “-able” is added to transitive verbs, and had a passive sense, but in EVS2 Tolkien said it could be added to intransitive verbs as well where it took on the sense of “able to” as in cálima “able to shine”. However, in LVS Tolkien clarified that there was a separate adjective suffix -ima that did not involve lengthening of the stem vowel, and served to form more generic adjectives:
-ima adjs. Only the adjs. in -ima found with long stem vowel were adjs. of possibility. -ima was frequently used with stems (verbal, adj[ectival] or nominal) with a short vowel, and the sense possessing to a high degree (at all times & by nature) the property mention[ed]. So kalima “luminous” (by nature always), vanima “beautiful, norima “running, swiftly a course[?]”, kelima “fluent”, istima “wise (in sense of knowing much), knowledgeable, very well informed”, melima “loving, very affectionate” — but lamélima “unlovable” (PE22/156).
Since the form in The Lord of the Rings was calima with short ă (LotR/720), it seems Tolkien abandoned the idea that such adjectives were connected to -ima “-able”. Indeed, the use of -ima as a general adjective suffix dates all the way back to Early Qenya and probably predates its use as a suffix of possibility: ᴱQ. korima “round”, ᴱQ. oilima “last”, ᴱQ. qolima “sickly, ailing”, etc.
-ite: The suffix -ite was used to describe a habit or intrinsic characteristic related to a verbal action such as: tirila “watching (something)” vs. tiríte “watchful, vigilant”; carila “doing, making (something)” vs. caraite “active, busy”.
Adjectives in íte or after omataima or last vowel of stem: aite, íte, oite, uite: are less defined in sense, the actual significance depending much on the verbal sense. An extension: vowel + maite is also frequent. Examples: karaite, karamaite, “able to make, handy, craftsmanlike, skilled”; tulumaite “likely to come, (of future events) probable”; himíte “clinging, able to stick on” (QVS, PE22/111).
iti, or combined with tense-vowels and other affixes generating more complex forms aiti, īti, uiti, etc., was not clearly defined in sense, but implied a habit or special association with the verbal action: khimīti: √KHIM “adhere”: “clinging, sticking, persistent, chronic” (QVS, PE22/137).
Ex. tiríte, keníte, xiete, karaite, koloite, yuluite, kuvoite from roots TIR “look at (turn eyes to, keep eyes on, watch)”, KEN “see”, SKEY “pass”, KAR “do”, KOL “bear, carry”, YUL “drink”, KUB “hide, secrete”. The senses differed from the participle in la in describing some general, natural or usual characteristic: thus tirila “watching (something)”, tiríte “watchful, vigilant”; similarly xiete “passing, impermanent”; karaite “active, busy” ... koloite ... “capable of bearing, tolerant (of), enduring” ... yuluite “drinking (as a habit)”, as in yuluiti kuimar [habitually drinking animals], fishes etc. ... kuvoite “hiding, secretive” (LVS, PE22/155).
Tolkien’s ideas on the exact meaning of this suffix developed over time. In the late 1940s, it’s exact meaning wasn’t fixed (karaite “able to make, handy, craftsmanlike, skilled”) but by the late 1960s had the more specific meaning of “describing some general, natural or usual characteristic”: caraite = “active, busy”. Perhaps the clearest way of describing this sense is as “generally or habitually Xing” where X is the verb. Thus:
- himíte: “generally or habitually adhering” = “persistent, chronic”.
- karaite: “generally or habitually doing” = “active, busy”.
- koloite: “generally or habitually bearing” = “tolerant (of), enduring”.
- kuvoite: “generally or habitually hiding” = “secretive”.
- tiríte: “generally or habitually watching” = “watchful, vigilant”.
As for how the adjective was formed, it was a combination of the stem + base vowel + -ite, so kar-a-ite, kol-o-ite, yul-u-ite. For base vowel i, the result was long í (tiríte) and likewise for stems with e since ei > í (keníte). Finally, since the sequence uvu was not favored, verbs stems with uv added -oite (kuvoite):
oite (from oiti and from uiti after v, by adaptation, since the sequence uvu was not favoured and unless altered became ú) (PE22/156).
-ula: The suffix -ula is for adjectives meaning “apt to do X” (active), as opposed to -ima which is “able to be Xed” (passive). It was discussed in QVS and EVS2, as well as in the early Quendian & Common Eldarin Verbal Structure (EVS1), but this suffix was not mentioned in later writing:
But [u] is also outside tense associated with the notion of “begin to do something now (completed later)” so in u-verbs: kelu “begin to flow”. Cf. also u-la adj. = “apt to, likely to do so” (EVS1, PE22/97).
Adjectives in ū̆la (in which the ū̆ is possibly related to the ū̆ seen in the futures) express likelihood, aptitude: similar to Latin “-āx”: nyárula “apt to talk, or relate”; kúvula “flexible, pliant” (QVS, PE22/111).
ū̆lā usually expressed likelihood or aptitude (in what would be the subject of the verb): matulā “edacious” (EVS2, PE22/137).
Distinguishing between -ite and -ula is a bit tricky, especially since -ula is not described in LVS, but it seems -ite refers to habitual (current or previous) activity as opposed to -ula that refers to potential (future) activity. In practice there was probably a fair about of ambiguity between the various suffixes, especially with intransitive verbs: “flexible” was given as both kúvula and kúvima (from the verb kuv- “bow”).
In QVS it seems that -ula requires lengthening of the stem vowel, much like -ima. This seems not be true in the one example given in EVS2, but that may well be an archaic (Common Eldarin) form. For purposes of Neo-Quenya I would assume -ula follows rules similar to -ima.