smutty adj.

1660s, "black mark, stain," from verb smutten "debase, defile" (late 14c.), later specifically "stain or mark made with soot, etc." (1580s), cognate with Middle High German smotzen "make dirty," from West Germanic *smutt- (source also of Middle High German smuz "grease, dirt;" German Schmutz "dirt," schmutzen "to make dirty").

The meaning "indecent or obscene language" is attested from 1660s. As the name of a fungous disease of plants, also 1660s. The verb in the figurative sense of "tarnish, defile" is from c. 1600.

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.