The Collaborative International Dictionary of English v.0.48:
Prothalamion \Pro`tha*la"mi*on\, Prothalamium \Pro`tha*la"mi*um\, n. [NL., fr. Gr. ? before + ? chamber, especially, the bridal chamber.] A song in celebration of a marriage. --Drayton. [1913 Webster]WordNet (r) 3.0 (2006):
prothalamion n 1: a song in celebration of a marriage [syn: prothalamion, prothalamium]