Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
praestĭno, āvi, ātum, 1, v. a. [1. praes], to buy, purchase (ante- and post-class.): ego eo in macellum, ut piscium quidquid ibi’st, pretio praestinem, Plaut. Ps. 1, 2, 36: piscis praestinatum abire, id. Capt. 4, 2, 68; cf.: praestinare apud Plautum praeemere est, i.e. emendo tenere, Paul. ex Fest. p. 223 Müll.: aliquid viginti denariis, App. M. 1, p. 113, 15: id omne praestinaturus, id. ib. 1, p. 104, 21 al.