Lewis & Short

Sympŏsĭum, ii, n., = Συμπόσιον (The Banquet), the title of one of Plato’s dialogues, Gell. 1, 9, 9; Quint. 8, 4, 23; Nep. Alcib. 2, 2.
A dialogue of Xenophon, Plin. 34, 8, 19, § 79.