Old English spillan "destroy, kill," variant of spildan, from Proto-Germanic *spelthijanan (cf. Old High German spildan "to spill," Old Saxon spildian, Old Norse spilla "to destroy," Middle Dutch spillen "to waste"), from PIE *spel- "to split, break off" (cf. Middle Dutch spalden, Old High German spaltan "to split;" for further cognates, see spoil). Related: Spilled; spilling.
Sense of "let (liquid) fall or run out" developed mid-14c. from use of the word in reference to shedding blood (early 12c.). Intransitive sense is from 1650s. Spill the beans recorded by 1910 in a sense of "spoil the situation;" to cry for spilt milk (usually with negative) is attested from 1738.
1845, originally "a throw from a horse," from spill (v.).