etymon

noun pl. -·mons′ or -·ma-mə

1. the earlier form of a word, as at an earlier period in the development of a language: in this dictionary etymons are shown in italic type within the etymologies Old English eage is the etymon of Modern English eye
2. a word or morpheme from which derivatives or compounds have developed

Etymology: L < Gr etymon, literal sense of a word, etymology, neut. of etymos, true < IE *seto- < base *es-, to be > is, L sum, est