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.
biltha-
verb. to flutter, flit
feltha-
verb. to resemble, seem like; to seem likely, be probable
A verb appearing as G. feltha- in the Gnomish Lexicon of the 1910s, glossed “resemble, seem like; seem likely, be probable” and based on G. fel “like” (GL/34).
Neo-Sindarin: Since I update G. fel to ᴺS. bîl “likeness, similarity”, I would update feltha- to ᴺS. biltha- “to resemble, seem like; to seem likely, be probable”. I would assume the “seem likely” sense is intrasive: sa biltha “that seems likely”, as opposed to transitive sa biltha herw “that seems like/resembles wine”.
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.
The verb G. biltha- “flutter, flit” appeared in the Gnomish Lexicon of the 1910s, an elaboration of G. bil “bird” (GL/23).
Neo-Sindarin: Since G. bil “bird” is no longer used, for purposes of Neo-Sindarin I would alter this verb to ᴺS. gwilwa- “to flutter, flit”, inspired by Q. wilwa “fluttering to and fro”.