a forlorn hope a faint remaining hope or chance; a desperate attempt.

☞ This expression developed in the mid 16th century from the Dutch expression verloren hoop 'lost troop'. The phrase originally denoted a band of soldiers picked to begin an attack, many of whom would not survive; the equivalent French phrase is enfants perdus 'lost children'. The current sense, which dates from the mid 17th century, arose from a misunderstanding of the etymology.