There are more words but they are from Tolkien's earlier conceptional periods. Tolkien likely changed these words as he evolved the aesthetics and completeness of the languages. You may even find languages that Tolkien later rejected. Do not mix words from different time periods unless you are familiar with the phonetic developments.
thin
root. *grey
tin
root. sparkle, emit slender (silver pale) beams
nindi
root. fragile, thin
slinyā
adjective. lean, thin, meagre
akrā
adjective. narrow
andā
adjective. long
span
root. white
tainā
adjective. long
terēn(ē)
adjective. slender
winyē
noun. evening
Below: Tolkien's Late Period (1950–1973). These are from Tolkien's late conceptual period — his most settled forms of the languages. Prefer these over the earlier ones above when composing new text.
A root in The Etymologies of the 1930s glossed “fragile, thin” with derivatives like ᴹQ. ninde/N. ninn “slender” (Ety/NIN-DI), replacing deleted ᴹ√NIN-DA “blue” (EtyAC/NIN-DI) which was probably a later manifestation of ᴱ√NINI “✱blue” from the Qenya Lexicon of the 1910s (QL/66). ᴱ√NINI had derivatives in both Qenya and Gnomish in the 1910s, but there are no signs of nin- as “blue” in Tolkien’s later writing.