S. final [i] intruded into preceding syllable; [-VCi] > [-ViC]

S. short final vowels vanished; [-S{ĕăŏ}] > [-Sø]

S. [ę̄] became [ai]; [ę̄] > [ai]

The Primitive Elvish long vowel [ę̄], a slacker and lower long [ē], developed into [ai] in Sindarin (PE18/96). A similar sound change occurred in Noldorin, except at that conceptual stage Tolkien represented the sound as [ǣ], with a slightly different pronunciation. Tolkien described this sound change in several places, with somewhat different details each time:

S. [ǭ] became [au]; [ǭ] > [au]

The Primitive Elvish long vowel [ǭ], a slacker and lower long [ō], developed into [au] in Sindarin (PE18/96). A similar sound change occurred in Noldorin, though the exact details of the phonetic development are different. Tolkien described this sound change in several places, with somewhat different details each time:

Si lúmissen yá hlarimme pá kelvaron *aufirie ilaures, taite sinyar *tatallálime. *Minaþurindor utúvier i Tolde Kalápakos *þandanasto ya queni navalyaner *aufirina tensi. Esserya ná *þandanasto Fernandina. Inya nasto náse ar minaþurindor navir kénai olane ambe epe loar tuxa; ente navinte amba imye þandanastor oiar ké i tolde, etta estel ea sa i kelvaron nóte ololluva tuluryasse.

*þandanasto noun "shield-beast, turtle, tortoise"

*aufir- verb "die off, die out, become extinct"

*minaþurindo noun "researcher"

S. [ŋ] vanished with compensatory lengthening; [Vŋ{nw}] > [V̄{nw}]

Tolkien mentioned that the nasal velar [ŋ] vanished in Sindarin with compensatory vowel lengthening on at least two occasions, both in conjunction with the etymology of S. têw or tîw “letter”:

S. [nm], [ŋm] became [nw], [ŋw]; [{nŋ}m] > [{nŋ}w]

There is evidence that in both Sindarin and Noldorin, the labial nasal [m] became [w] after another nasal, [n] or [ŋ]. This sound change is mentioned in some notes from the late 1960s on the phonetic developments of combinations of nasals:

NOTE: Edited to reflect timing issues, on whether this change took place before or after i-affection, and the implications on plural forms.

S. [x], [ɸ] vocalized between a vowel and [s], [θ]; [Vx{θs}|Vɸ{θs}] > [Vi{θs}|Vu{θs}]

NOTE: Edited to reflect different Sindarin vocalization of [ŋ] (vanishing with compensatory lengthening).

S. [ɣ] vocalized before [l], [r], [m], [n]; [V{ɣ}{lrmn}] > [Vi{lrmn}]