Translation guide
A shirt worn with the top button(s) undone, leaving the neck exposed. In Japanese, this is typically described rather than named with a single common noun.
The speaker wants to describe a shirt worn with the collar open, often in a casual or relaxed style.
Literally 'a shirt with the collar opened'. This is the most direct and natural way to describe an open-necked shirt.
彼は襟を開けたシャツを着ていた。
He was wearing an open-necked shirt.
Literally 'a shirt with buttons undone'. Focuses on the action of unbuttoning, often implying the top button(s).
The speaker refers to the style itself, often in fashion contexts.
Loanword from English 'open collar shirt'. Common in fashion and retail, refers to shirts designed to be worn open at the neck.
この夏はオープンカラーシャツが流行っている。
Open-necked shirts are trendy this summer.
Japanese does not have a single everyday word for 'open-necked shirt'. Instead, describe the state of the shirt (e.g., 襟を開けた) or use the fashion term オープンカラーシャツ.
Because it was hot, I went out in an open-necked shirt.
Specifically 'a shirt with the first button undone'. More precise, but less common in casual speech.
面接では第一ボタンを外したシャツは避けたほうがいい。
It's better to avoid an open-necked shirt for an interview.
Literally 'open collar shirt'. A more Japanese-sounding term, used in fashion but slightly less common than the loanword.
開襟シャツはリラックスした印象を与える。
Open-necked shirts give a relaxed impression.