βεβαιωτής

οῦ, ὁ
A. one who gives assurance of a thing, authority, ἀμφισβητουμένων Plb. 4.40.3 (pl.); ἱστορίας D.H. 1.28, cf. 3.67, al.; confirmatory, λόγοι Phld. Sign. 29.
2. legal surety, τοῦ μόνιμον τὴν ὁμόνοιαν γενέσθαι Plb. 2.40.2; β. τῆς πίστεως παρέχεσθαι Plu. Flam. 4; warrantor in sales, SIG 2832 (Amphipolis), etc.
Liddell, Scott & Jones
A Greek-English Lexicon, 1940
An open-access project