[Middle English espousaille, from sing. of Old French espousailles, betrothal, from Latin spōnsālia, from neuter pl. of spōnsālis, of a betrothal, from spōnsus, spouse; see spouse.]
1393, from O.Fr. espousailles (pl.) "act of betrothal," from L. sponsalia, neut. pl. of sponsalis "of a betrothal," from sponsa "spouse." Espouse is 1435; extended sense of "adopt, embrace" (as a cause) is 1622. For the -e- see especially.