An adjective for “sickly” in The Etymologies of the 1930s from the root ᴹ√GENG-WA “sick” (Ety/GENG-WĀ), where the ancient cluster *ngw* became *mb* as usual in Noldorin and Sindarin.
Noldorin
flaew
adjective. sickly, sick, ill
flaew
adjective. sickly, sick, ill
thlaew
adjective. sickly, sick, ill
gem
adjective. sickly
gem
adjective. sickly
gemb
adjective. sickly
thloew
adjective. sickly, sick, ill
An adjective appearing as N. flaew “sickly, sick, ill” in The Etymologies of the 1930s derived from ON. thlaiwa < ᴹ✶slaiwā under the root ᴹ√SLIW “sickly” (Ety/SLIW). The ancient initial *sl* became *thl* which was the usual sound change in (Old) Noldorin, and then this *thl* became *fl*, a less common Noldorin sound change. Tolkien wrote an intermediate form thlaew between ON. thlaiwa and N. flaew, but then revised this form to thloew, reflecting some uncertainty on the phonetic development of *ai* in Noldorin. There was also a deleted variant of this root: ᴹ√LIW, where Tolkien had lhaew “ill” with the usual unvoicing of initial *l* in Noldorin (EtyAC/LIW).
Neo-Sindarin: In Sindarin of the 1950s and 60s, initial *sl* became *lh* instead of thl, so most Neo-Sindarin writers adapt this word as ᴺS. lhaew “sickly, sick, ill”, as suggested by HSD (HSD).