In both Sindarin and Noldorin, any non-initial [h] vanished after vowels, as noted by David Salo (GS/§4.100, GS/§4.107, GS/§4.116). A similar sound change occurred in Welsh (WGHC/§94ii). This sound change primarily applied to the [h] that developed from intervocalic [s] which therefore ultimately vanished, as described by Tolkien in a note in The Etymologies from the 1930s:

N. dis “bride” cannot be direct for ON. dis since medial and final s were lost in Exilic Noldorin (EtyAC/NDIS).

This sound change was also described in the Comparative Tables of phonetic development from the 1930s: s > ON. s > N. h, - (PE19/23), with the “-” indicating a vanishing sound. There are numerous examples in both Sindarin and Noldorin:

• ✶tindōmi-sel(dĕ) > tindúmhihel > S. Tinnúviel “Nightingale” (PE19/73).
• ᴹ√NUS > nusina > ON. nuhina > nohen > N. noen “wise, sensible” (EtyAC/NUS).
• ᴹ✶barasā́ > barasa > ON. baraha > N. bara “fiery, eager” (Ety/BARAS).
• ᴹ✶khyelesē > khelesa > ON. kheleha > N. hele “glass” (Ety/KHYEL(ES)).

The net result of this sound change was that isolated non-initial s could not appear in Sindarin except finally as a reduction of [ss]. The ultimate loss of [s] in Sindarin and Noldorin could lead to some interesting effects at the end of words. In particular, it could lead to some irregular plurals where a vowels was lost in the singular form but preserved in the plural by an [h] that later vanished:

• S. thôl “helmet”, plural thely (PE17/188): *tholosi > *tholuhi > *thœlyh > thely.
• N. pêl “fenced field”, plural peli (Ety/PEL(ES)): *pelesi > *pelihi > peli.

These plurals were sometimes reformed to more regular forms. For example, S. thôl also has an alternate plural thuil, which is the more common plural pattern for monosyllables with long ô.

Note that medial isolated h could appear in compounds as the soft mutation of s, indicating the loss of [h] was no longer an active phonetic rule in Sindarin: S. Eglahir = (probably) Egla- + sîr (WJ/117), S. Nanduhirion = nan(d) + dû + sîr + -ion (PE17/37).

The timing of this sound change is difficult to nail down. S. lhaw < (ancient dual) *slasū indicates the h must have vanished before the loss of final u (PE17/62), since the u survived long enough to form a diphthong. However, there are other examples that indicate a later loss, like past form ahawv > au of the verb sav- (PE17/173) and the archaic form tindúmhihel of Tinnúviel (PE19/73).

There are a few examples of intervocalic h surviving in Sindarin: ahamar “neighbor” (VT48/20) and arahadhw “throne” (PE22/148). These could be archaic, or it could be that intervocalic h survived if it prevented otherwise awkward vowel combinations.

Conceptual Developments: The example ᴱ✶ı̯aisa > G. gais (GL/37) indicates that this sound change was not part of Gnomish in the 1910s; this is further supported by the fact that the soft mutation of s to h did not appear in the Gnomish Grammar (PE11/7). This soft mutation also did not appear in the Early Noldorin Grammar of the 1920s (PE13/121). However, in the Early Noldorin word lists, there are several examples of intervocalic [s] vanishing, as noted by Roman Rausch in his Historical Phonologies of Ilkorin, Telerin and Noldorin around 1923 (HPITN/§4.1.3):

• ᴱ✶pelesa > ᴱN. helai “fence” (PE13/147).
• ᴱ✶t:loise > ᴱN. tlui “slender” (PE13/154).
• ᴱ✶tésare > ᴱN. teiar “brick” (PE13/153).

At this conceptual stage there seem to be some additional vocalic effects associated with the disappearance of s/h, but determining the exact rules from the small set of samples is difficult. It is very likely [s] passed through [h] before vanishing in Early Noldorin, so it seems Tolkien introduced this sound change sometime in the 1920s.

GS/§4.100 GS/§4.107 GS/§4.116 WGHC/§94ii [Kelt s > Brit h > W ø; medially between vowels] @@@