prodigious (adj.)

mid-15c., prodige, "a sign, portent, something extraordinary from which omens are drawn," from Old French prodige and directly from Latin prodigium "prophetic sign, omen, portent, prodigy," from pro "forth, before" (see pro-) + -igium, a suffix or word of unknown origin, perhaps from the same source as aio "I say" (see adage) or agere "to drive" (de Vaan), from PIE root *ag- "to drive, draw out or forth, move").

Meaning "person or thing so extraordinary as to excite wonder or astonishment" is from 1620s; the specific meaning "child with exceptional abilities" is by 1650s. Related: Prodigial.