μεσεγγῠ-άω · mesengy-aō — LSJ
deposit a pledge in the hands of a third party, in Pass., τρία τάλαντα μεσεγγυηθέντα being so deposited, Lys. 29.6:—Med., μεσεγγυήσασθαι ἀργύριον have oneʼs money deposited in the hands of a third party, D. 39.3, cf. Antipho 6.50.