ingrate n.

word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."

In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.

gwerə-, Proto-Indo-European root meaning "to favor."

It forms all or part of: agree; bard (n.); congratulate; congratulation; disgrace; grace; gracious; grateful; gratify; gratis; gratitude; gratuitous; gratuity; gratulation; ingrate; ingratiate.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit grnati "sings, praises, announces;" Avestan gar- "to praise;" Lithuanian giriu, girti "to praise, celebrate;" Old Celtic bardos "poet, singer."

mid-14c., from Old French ingratitude "ungratefulness" (13c.) and directly from Late Latin ingratitudinem (nominative ingratitudo) "unthankfulness," noun of quality from Latin ingratus "ungrateful" (see ingrate).