early 15c., from weed + -y (2). In old slang, in reference to horses, "not of good blood or strength, scraggy, worthless for breeding or racing," from 1800; hence, of persons, "thin and weakly" (1852).
"plant not valued for use or beauty," Old English weod, uueod "grass, herb, weed," from Proto-Germanic *weud- (source also of Old Saxon wiod, East Frisian wiud), of unknown origin. Also applied to trees that grow abundantly. Meaning "tobacco" is from c. 1600; that of "marijuana" is from 1920s. The chemical weed-killer is attested by 1885.
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).
<a href="https://www.etymonline.com/word/weedy">Etymology of weedy by etymonline</a>
Harper, D. (n.d.). Etymology of weedy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/weedy