RhymeZone: perdu definitions

Definitions of perdu:

adjective: (obsolete, military) Stationed in an exposed or hazardous position; hidden in ambush. Originally as sentinel perdu.
adjective: (now rare) In a dangerous situation; lost, desperate.
adjective: (now rare) Hidden; concealed from sight. Chiefly with lie.
noun: One placed on watch, or in ambush.
noun: A soldier sent on a forlorn hope.

(Definitions from Wiktionary)