Gnomish
cwîl
adjective. quiet, peaceful, gentle
cwel-
verb. to fade, wither
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!
An adjective appearing as G. {cwild >>} cwîl “quiet, peaceful, gentle” in the Gnomish Lexicon of the 1910s (GL/28). It is clearly related to ᴱQ. qilda “quiet, hushed, still” based on the early root ᴱ√QḶŘḶ [QḶÐḶ] (QL/78).
Neo-Sindarin: For purposes of Neo-Sindarin I would adapt this word as ᴺS. pell fitting the Sindarin phonetic developments from primitive ✱kwildā as originally suggested by Fiona Jallings, but Fiona gave it the same gloss as its Early Qenya equivalent, whereas I would use the glosses “quiet, peaceful, gentle” from Gnomish.