mid-15c., "fruitful, abundant," from seed (n.) + -y (2). From 1570s as "abounding in seeds." Meaning "shabby" is from 1739, probably in reference to the appearance of a flowering plant that has run to seed. Related: Seediness.
Old English sed, sæd "that which may be sown; an individual grain of seed; offspring, posterity," from Proto-Germanic *sediz "seed" (source also of Old Norse sað, Old Saxon sad, Old Frisian sed, Middle Dutch saet, Old High German sat, German Saat), from PIE *se-ti- "sowing," from root *sē- "to sow." Figurative use in Old English. Meaning "offspring, progeny" rare now except in biblical use. Meaning "semen" is from c. 1300. For sporting sense, see seed (v.).
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 seedy. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/seedy