【Ambush】 and 【ambuscade】 both mean a device to entrap an enemy by lying in wait under cover for an opportune moment to make a surprise attack.
【Ambush】 , however, is also used to designate an act of lying in wait or in concealment (as for spying, frightening, or obtaining an advantage); when used of nonmilitary activity it sometimes connotes unfairness or cowardliness.
ambushes of cutthroats —Thackeray
when he was a boy he had . . . spied on the Pecos men . . . . He had lain in 【ambush】 for two nights on the mountain —Cather
【Ambuscade】 usually implies the legitimate strategic disposition of troops in concealment, but in military use is more often applied to the body of troops or to their position than to the trap.
the knights and gentlemen volunteered for an 【ambuscade】 to cut off the convoy —Froude
feared in every wavering brake an 【ambuscade】 —Tennyson
