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 (see expand). 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.