Lewis & Short

antestor, ātus, 1, v. dep [acc. to Corssen, Ausspr. II. p. 564, from an-, the Gr. ἀνά, as in anhelo, q. v. fin., and testor; acc. to others, from ante and testor], a word peculiar to judicial proceedings, to call up as a witness before the opening of the cause, to call as a witness (the formula was: licet antestari? and the person gave his assent by offering the tip of his ear, which the summoner touched; cf. Smith, Dict. Antiq.); so in 1 Fragm. in XII. Tab.: SI. IN. IVS. VOCAT. NI. IT. ANTESTATOR. IGITVR. EM. CAPITO: Ph. Licet te antestari? Th. Non licet, Plaut. Curc. 5, 2, 23; cf. id. ib. 5, 2, 25; id. Pers. 4, 9, 10; so id. Poen. 5, 4, 59; 5, 4, 60: magnā Inclamat voce, et Licet antestari? Ego vero Oppono auriculam, * Hor. S. 1, 9, 76: est in aure imā memoriae locus, quem tangentes antestamur, Plin. 11, 45, 103.
In Cic. once, in gen. sense, not pertaining to judic. proceedings: te, magne, antestaretur, quod nunc etiam facit, Mil. 25 fin.
In a pass. signif., Liv. Andron. ap. Prisc. p. 792 P.
Hence, antestātus, a, um, P. a.; subst., a witness, Gai. Inst. 1, 6, 3.