申し訳
もうしわけ · moushiwake · JLPT N3 · noun
apology
申し訳 = humbly say (申す) + reason (訳): a humble explanation
申す is the humble verb for say, and 訳 means reason. So 申し訳 is the reason you humbly offer. Add ない (none) and 申し訳ない literally means I have no excuse, which is a formal way to say sorry.