Lewis & Short

sponsĭo, ōnis, f. [spondeo], jurid. and publicists’ t. t., a solemn promise or engagement to some performance (in bargains, covenants, treaties, etc.); a promise, guarantee, security, sponsion for any one (freq. and class.; cf.: pactio, foedus).

  1. I. In gen.: sponsio appellatur omnis stipulatio promissioque, Dig. 50, 16, 7: voti sponsio, quā obligamur deo, Cic. Leg. 2, 16, 41: Scandilium cogis sponsionem acceptam facere, id. Verr. 2, 3, 60, § 139: per inducias sponsionem faciunt, uti, etc., made an agreement, Sall. J. 79, 4: non foedere pax Caudina sed per sponsionem facta est, by giving surety, Liv. 9, 5, 2: sponsione se obstringere, id. 9, 8, 4: sponsionem interponere, id. 9, 9, 4; and: tunc sponsio et pax repudietur … nec populus Romanus consulum sponsionem nec nos fidem populi Romani accusemus, id. 9, 11, 5: Ocriculani sponsione in amicitiam accepti, id. 9, 41, 20; 39, 43, 5 (but Plaut. Trin. 2, 4, 26, is spurious; v. Ritschl ad h. l.).
  2. II. In partic., in civil suits, a mutual agreement or stipulation of the parties, that he who loses should pay a certain sum to him who gains the cause, a sort of wager at law: per sponsionem hoc modo agimus; provocamus adversarium tali sponsione: si homo quo de agitur ex jure Quiritium meus est, sestertios XXV. nummos dare spondes? Gai. Inst. 4, 93: condicio Quintio fertur, ut, si id factum negaret ceteraque, quae objecisset, sponsione defenderet sese, Liv. 39, 43, 5: in probrum suum sponsionem factam, id. 40, 46, 14; hence, sponsio (sponsionem facere) si non (ni), a wager that, to agree to make a payment if not: ut sponsionem facere possent, ni adversus edictum praetoris vis facta esset, Cic. Caecin. 16, 45: sponsio est, ni te Apronius socium in decumis esse dicat, id. Verr. 2, 3, 59, § 135: sponsionem milium nummūm facere cum lictore suo, ni furtis quaestum faceret, id. ib. 2, 5, 54, § 131; cf.: jubet Quinctium sponsionem cum Sex. Naevio facere, si bona sua ex edicto dies XXX. possessa non essent, id. Quint. 8, 30; id. Fam. 7, 21 init.; id. Pis. 23, 55: sponsione optime facere posse, id. Caecin. 16, 45; id. Off. 3, 19, 77: Apronium sponsione lacessivit, id. Verr. 2, 3, 57, § 132: sponsione vincere, id. Quint. 27, 84.
    Post-class., with quod: de sponsione quam is cum adversario, quod vir bonus esset, fecerat, Val. Max. 7, 2, 4: sponsionem provocare, quod, etc., id. 2, 8, 2; 6, 1, 10.
    With acc. and inf.: Cleopatra sponsione revocavit, insumere se posse, etc., Macr. S. 2, 13.
      1. 2. Hence, in gen., a bet, betting: audax, Juv. 11, 202.
    1. B. Meton., a sum of money deposited according to agreement, a stake, acc. to Varr L. L. 6, § 70 Müll.