creepy adj.

Old English creopan "to move the body near or along the ground as a reptile or insect does" (class II strong verb; past tense creap, past participle cropen), from Proto-Germanic *kreupanan (source also of Old Frisian kriapa, Middle Dutch crupen, Old Norse krjupa "to creep"), perhaps from a PIE root *g(e)r- "crooked" [Watkins].

From c. 1300 as "move secretly or to evade detection," also "move slowly, feebly, or timorously." In reference to imperceptible movements of things (soil, railway rails, etc.) from 1870s. Related: Crept; creeping.

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). Adjectives such as hugy, vasty are artificial words that exist for the sake of poetical metrics.