ἐπιμαρτύρεσθαι
From LSJ
Greek > English (Woodhouse Verbs Reversed)
(see also ἐπιμαρτύρομαι): conjure, invoke, call in as witness, call on as witness, call on, call to witness, call upon
Lexicon Thucydideum
obtestari, to beseech, 6.29.2 (de Alcibiade concerning Alcibides).