Word Origin & History
pp. suffix of weak verbs, from O.E. -ed, -ad, -od (leveled to -ed in M.E.), from P.Gmc. *-do-, from PIE *-to- (cf. Gk. -tos, L. -tus). Originally fully pronounced, as still in beloved (which, with blessed, accursed, and a few others retains the full pronunciation through liturgical readings). In 16c.-18c.
often written -t when so pronounced (usually after a consonant or short vowel), and still so where a long vowel in the stem is short in the pp. (crept, slept, etc.). In some older words both forms exist, with different shades of meaning, cf. gilded/gilt, burned/burnt.