Middle Primitive Elvish
slaiwā
adjective. sickly, sick, ill
gengwa
root. sick
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
A root in The Etymologies of the 1930s glossed “sick” with derivatives ᴹQ. engwa/N. gem “sickly” (Ety/GENG-WĀ). It was given as ᴹ√GENG-WĀ, and thus represented an extension of an otherwise unattested root ᴹ√GENG. In the entry for ᴹ√YEN from The Etymologies it appeared as ᴹ√GEM in the discussion of N. ingem “old, (lit.) year-sick” (EtyAC/YEN), but I believe this represents the Noldorin phonetic developments of the true primitive form rather than a conceptual variation. The continued appearance of Q. Engwar in The Silmarillion narratives of the 1950s and 60s hints that this root may have remained valid as well.