Flattering

google

ref

Middle English: perhaps a back-formation from flattery.

wiktionary

ref

From Middle English flatering, flatrung(gerund), equivalent to flatter +‎ -ing.

etymonline

ref

flattering (adj.)

late 14c., "pleasing to the imagination; dishonestly pleasing; having a false appearance of favorableness," present-participle adjective from flatter. Meaning "gratifying to self-esteem" is from 1757. Related: Flatteringly.