The earliest word for “food” in precursors to the Sindarin language was G. môs “food (of men)” (GL/56, 58), probably based on the early root ᴱ√M(B)ASA “cook, bake” (QL/59). This became ᴱN. math “food” in Early Noldorin Word-lists of the 1920s, appearing only in its lenited form vath as an element in ᴱN. orvath “foodless” (PE13/155). In The Etymologies of the 1930s Tolkien had N. mann “food” as a derivative of primitive ᴹ✶matna under the root ᴹ√MAT “eat”, but the version of the entry where this form appeared was struck out (EtyAC/MAT). The primitive form ✶matnā “food” did reappear in the early 1950s, however (PE22/136).

Neo-Sindarin: Of the above, I prefer ᴺS. math for “food”. I first saw math proposed as the Neo-Sindarin word for “food” in a list of neologisms by Elaran on the Vinyë Lambengolmor Discord Server (VLDS) from 2018. I prefer math because I tend to assume Q. matta is derived from *mattā rather than ✶matnā to avoid certain phonological difficulties; see that entry for discussion. If you are not concerned with those difficulties, ᴺS. mann “food” is also viable.