The punctuation in The Etymologies is considered incorrect (the full dot after this word should conceivably be a comma)
Noldorin
thinn
adjective. grey, pale
thinn
adjective. grey, pale
thinna-
verb. to fade, *(lit.) become grey
thinnas
noun. shortness, shortening
thind
adjective. grey, pale
thinna-
verb. to fade, to grow towards evening
thinnas
noun. lit. "shortness" (name of a mark indicating short quality of vowel)
thinnas
noun. shortening, sign of short vowel
thîn
noun. evening
thîn
noun. evening
thent
adjective. short
gwinna-
verb. to fade
gwîn
noun. evening
mid
adjective. grey
mith
adjective. (pale) grey
mith
adjective. grey
thent
adjective. short
A verb in The Etymologies of the 1930s glossed “fade” derived from ON. thintha- under the root ᴹ√THIN having to do with grey things (Ety/THIN), so perhaps more literally “✱become grey”.