The Collaborative International Dictionary of English v.0.48:
Ambush \Am"bush\ ([a^]m"b[oo^]sh), n. [F. emb[^u]che, fr. the
verb. See Ambush, v. t.]
1. A disposition or arrangement of troops for attacking an
enemy unexpectedly from a concealed station. Hence: Unseen
peril; a device to entrap; a snare.
Heaven, whose high walls fear no assault or siege
Or ambush from the deep. --Milton.
2. A concealed station, where troops or enemies lie in wait
to attack by surprise.
Bold in close ambush, base in open field. --Dryden.
3. The troops posted in a concealed place, for attacking by
surprise; liers in wait. [Obs.]
The ambush arose quickly out of their place. --Josh.
To lay an ambush, to post a force in ambush.