a Sicilian game ... much in vogue at the drinking parties of young men at Athens. The simplest mode was when each threw the wine left in his cup, so as to strike smartly in a metal basin, at the same time invoking his mistress' name; if the whole fell with a distinct sound into the basin, it was a sign he stood well with her .... The game soon became complicated and was played in various ways. [Liddell and Scott, "Greek-English Lexicon," 1901]
Beeks writes that kottabos "indicated not only the game itself, but also several objects and movements used in it," so, "[a]s the original meaning of [kottabos] is unknown, all etymologies are necessarily uncertain."
There also was a denominative verb, kottabizein, "to play kottabos," also euphemistic for "to vomit."