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to open (e.g. one's robe); to bare (e.g. one's chest); to expose
to open up (of clothing); to be exposed
寝ている間にシャツがはだけた。
My shirt came open while I was sleeping.
ボタンが外れてはだけちゃった。
The button came off and it opened up.
風ではだけないように押さえた。
I held it down so it wouldn't come open in the wind.