This adverb means 'in Gentile fashion' or 'like the nations'—behaving according to non-Jewish customs rather than Torah observance. In Galatians 2:14, Paul confronts Peter for compelling Gentiles 'to live like Jews' when Peter himself sometimes lived 'like a Gentile' (the implied contrast). The word derives from 'ethnikos' (national, gentile), and the adverbial form describes conduct characteristic of non-Jews. The multilingual evidence (Spanish 'gentílicamente', German 'heidnisch' = pagan-like) captures this ethnic-cultural behavioral distinction between Jewish and Gentile lifestyle.