There is no evidence that Tolkien consider monosyllabic nouns as a distinct class in his later writings, but such nouns are more likely to be irregular than other nouns, since they represent more basic concepts. For example, the noun má “hand” does not have a plural form *már or *mái, but uses only the partitive plural máli (VT47/6). Independent pronouns are also generally monosyllabic, so they would be declined like members of this group.

Tolkien generally referred to nouns ending in a consonants as “consonantal” nouns, for example on PE14/42 (1920s) and PE21/76 (1950s). As with all Quenya words, a noun can only end in one of the five valid final consonants: l, n, r, s, t. Consonantal nouns were often a reduction of longer ancient forms, however, and their inflections could reflect these more ancient endings.

(I've taken a look into this matter - and the notes that I've been making during the process have piled up considerably. So let me share them here for the potential future reference; maybe someone will find them interesting.)
 

One special subgroup of vocalic nouns are those that end in the vowel e, or “e-nouns”. Frequently these have inflection suffixes identical to those of other vocalic nouns, but they differ significantly in plural forms. In particular, they do not (normally) use the plural suffix -r, but instead form their plurals by changing their final e to i. The details of these forms and their historical developments is discussed in the entries on plural nouns and for the individual noun cases.

Tolkien generally referred to nouns ending in a vowels as “vocalic” nouns, for example on PE14/42 (1920s) and PE21/76 (1950s). Nouns can end in any of the five vowels: i, e, a, o, u. Since many noun inflections begin with a consonant, such inflections simply add the suffix to the final vowel of the noun:

Posted out of order because I wanted to write up noun cases before noun classes. Things will be in the correct order in the next Eldamo release.

The comitative case is one that Tolkien abandoned in his later writings. Indeed, the function of this case is not entirely clear, though its name implies that it indicates an “accompanying” noun. In its first appearance, the comitative case used the suffix -iko (PE16/113), and in this form it may have appeared in some sentences from the earliest drafts of the Markirya poem, as suggested by the editors of PE16 (Gilson, Smith, Wynne, Hostetter and Welden):

This noun case is one that Tolkien abandoned in his later writings. In the Early Quenya Grammar (EQG) he called it the “Manner” case (PE14/46, 78), but in declension tables from the late 1920s through 1930s he often labeled it the “Adverb” case (PE16/113; PE21/4, 53) and in a couple places he called it the “Comparative” case (PE21/42, 46).