for one thing

US /fɔːr wʌn θɪŋ/
UK /fɔːr wʌn θɪŋ/
"for one thing" picture
1.

まず第一に, 一つには

used to introduce one reason, among others, for something

:
I can't go out tonight; for one thing, I have to study.
今夜は出かけられない。まず第一に、勉強しなければならない。
Why didn't you tell me? Well, for one thing, you were busy.
なぜ教えてくれなかったの?ええと、まず第一に、あなたは忙しかったから。