Extended Strong's Greek Lexicon (Abbott-Smith based)
be convinced
Usage: πιστόω, -ῶ (πιστός), [in LXX chiefly for אָמֵן ni. ;] to make trustworthy (Thuc., 3Ki.1:36), hence, to establish (1Ch.17:14). Pass. and mid., to be assured of: with accusative of thing(s), 2Ti.3:14.† (AS)