1914, from colloquial verb smalm, smarm "to smear, bedaub" (the hair, with pomade), 1847, of unknown origin, perhaps somehow suggestive of the action. Verbal meaning "to smear with flattery" is from 1902.
adjective suffix, "full of or characterized by," from Old English -ig, from Proto-Germanic *-iga- (source also of Dutch, Danish, German -ig, Gothic -egs), from PIE -(i)ko-, adjectival suffix, cognate with elements in Greek -ikos, Latin -icus (see -ic). Originally added to nouns in Old English; used from 13c. with verbs, and by 15c. even with other adjectives (for example crispy).
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Harper, D. (n.d.). Etymology of smarmy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/smarmy