What does "nonce" mean?

Nonce: The one or single occasion; the present call or purpose; -- chiefly used in the phrase for the nonce. The miller was a stout carl for the nones. Chaucer. And that he calls for drink, I 'll have prepared him A chalice for the nonce. Shak. Nonce word, "a word apparently employed only for the nonce". Murray (New English Dict. ).