Lewis Short
stĭpŭlātor (noun M) : stipulor, jurid. t. t.
* One who demands a formal promise or covenant (opp. promissor, the one who gives the promise); a bargainer, stipulator, Dig. 2, 10, 3; 45, 1, 41 sq.; 45, 38, 5; Suet. Vit. 14; Isid. Orig. 10, 5.
Charlton T. Lewis, Charles Short, A Latin Dictionary