Early Quenya
filqe
noun. fern
filinqe
noun. fern
filimpe
noun. fern
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.
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 word appearing as ᴱQ. filqe “fern” in the Qenya Lexicon and Poetic and Mythological Words of Eldarissa of the 1910s, with variants filinqe and (dialectical) filimpe [probably Solosimpi/Telerin], all derived from the early root ᴱ√FILI “fine, thin” (QL/38).
Conceptual Development: The Declension of Nouns (DN) of the early 1930s had ᴹQ. filet (filek-) with glosses {“fern” >>} “cobweb” (PE21/33 note #123), and in later writings filit (filik-) was a word for “small bird, sparrow” (Ety/PHILIK; PE21/56).
Neo-Quenya: Since there are no later non-rejected words with this meaning, I would retain ᴺQ. filquë “fern” for purposes of Neo-Quenya.