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.
gantha
adverb. more
ganthan
adjective. waxen, grown big, grown up, adult, [originally?] large
gân ar gantha
*young and old, (lit.) young and adult
gaid
adverb. more
A word for “more” in the Gnomish Lexicon of the 1910s related to the prefix G. ga- “very, more” (GL/36).
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 word G. {gantha >>} ganthan “(large), waxen, grown big, grown up, adult” appeared in the Gnomish Lexicon of the 1910s based on G. gant “larger” (GL/37). I believe the parenthetical “(large)” indicates its ancient meaning and “waxen, grown big, grown up, adult” is its modern meaning.
Neo-Sindarin: Since I retain ᴺS. gant for purposes of Neo-Sindarin as a derivative of the Neo-Root ᴺ√GYANTA, I would retain and adapt its enlargement as ᴺS. gannan “waxen, grown big, grown up, adult”, originally just “†large”.