c. 1400, intransitive, from Anglo-French espaundre, Old French espandre "to spread out, pour out, scatter, strew, spawn (of fish)" (Modern French épandre), from Latin expandere "to spread out, unfold, expand," from ex "out" (see ex-) + pandere "to spread, stretch" (from nasalized form of PIE root *pete- "to spread"). The notion is of a "spreading out" of fish eggs released in water. The transitive meaning "to engender, give rise to" is attested from 1590s. Related: Spawned; spawning.
late 15c., "fish eggs," from spawn (v.); figurative sense of "brood, offspring," and, insultingly, of persons, is from 1580s.