"blocky, ungraceful," by 1968 (when it was the name of a style of women's shoe), from clunk + -y (2). Related: Clunkily; clunkiness.
Entries linking to clunky
clunk v.
1796, "to make the sound of a cork being pulled from a bottle;" imitative. This was the main sense through most of 19c. Meaning "to hit, strike" is attested from 1943 (perhaps a variant of clonk). Related: Clunked; clunking. As a noun, in reference to the cork-pulling sound, by 1823.
-y 2
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.