A surprise attack by people lying in wait in a concealed position. As a verb, to attack by ambush.
From Old French 'embuscher' meaning 'to place in a wood', from 'en-' (in) + 'busch' (bush, wood). The military tactic and the word entered English in the 14th century from French military terminology.
The most famous ambush in American history might be the Boston Tea Party - though we don't usually think of it that way, the colonists essentially ambushed British tea ships under cover of disguise and darkness. Modern military doctrine still considers ambush one of the most effective tactics for smaller forces against larger ones, because it multiplies the psychological impact beyond the physical damage.
Complete word intelligence in one call. Free tier — 50 lookups/day.