Lewis Short
astĭpŭlātor | adst- (noun M) : (), , id..
* One who joins another in a stipulation, Gai Inst. 3, 110; so id. ib. 3, 117.—Hence
* An assistant in a trial, in gen.: testes tot ... cum adstipulatore tuo comparabuntur?Cic. Quint. 18, 58; so id. Pis. 9.—And trop., one who assents to or agrees with: illud falsum esse et Stoici dicunt et eorum adstipulator Antiochus,Cic. Ac. 2, 21, 67: vanae opinionis,Val. Max. 7, 1 fin.
Charlton T. Lewis, Charles Short, A Latin Dictionary