noun, adverb
once; one morning; temporarily; short period
Often used in set phrases like 一朝一夕 (in a short period) or 一朝事あるとき (should something happen). As a standalone noun/adverb, it can mean 'one morning' or 'once', but it is somewhat literary and less common in everyday speech.
一朝一夕にはできない。
It cannot be done in a short period.
一朝事あるときは、すぐに連絡してください。
Should something happen, please contact me immediately.