The verb for “to eat” derived from the root √MAT of the same meaning (PE17/131; Ety/MAT). In Tolkien’s later writing it appears only in inflected forms, but the verb itself is well established, dating back all the way to G. mad- in the Gnomish Lexicon of the 1910s (GL/56). This verb was one Tolkien often used in examples of verb conjugations and as such its inflected forms changed considerably over time, but that is more a topic of the evolution of the Sindarin verb system.
Sindarin
madu
madu
madu
?. [unglossed]
maud
?. [unglossed]
mad-
verb. to eat
madui
adjective. edible
cidinn
?. [unglossed]
cinnog
?. [unglossed]
>> maud. This gloss was rejected.