וַיַּ֧עַן עָכָ֛ן אֶת־יְהוֹשֻׁ֖עַ וַיֹּאמַ֑ר אָמְנָ֗ה אָנֹכִ֤י חָטָ֙אתִי֙ לַֽיהוָה֙ אֱלֹהֵ֣י יִשְׂרָאֵ֔ל וְכָזֹ֥את וְכָזֹ֖את עָשִֽׂיתִי׃
아간이 여호수아에게 대답하여 가로되 참으로 나는 이스라엘 하나님 여호와께 범죄하여 여차 여차히 행하였나이다
Radak
וגם אמנה, besides she is indeed my sister. The expression אמנה is equivalent to באמת, “in truth.” The word occurs in the same sense in Joshua 7,20 אמנה חטאתי, where Achan admits having stolen from the booty of Jericho. The word אמנם or אמנה both mean basically the same. Avraham in effect told Avimelech: “even though I did not protest the violence committed against Sarah this does not make me a liar, as she is indeed my sister, being the daughter of my brother, Legally, nieces are just as children as grandchildren are considered as legally equivalent to children.” (compare Rashi.