prothalamium
Concise Oxford English Dictionary © 2008 Oxford University Press:
prothalamium /ˌprəʊθəˈleɪmɪəm/
▶noun (pl. prothalamia /-mɪə/) literary a song or poem celebrating a forthcoming wedding.
– origin C16: from Prothalamion, the title of a poem by Spenser, on the pattern of epithalamium.
'prothalamium' also found in these Oxford entries:

