noun
A person who is present to observe and verify an event, such as a contract signing, examination, or official procedure. Often used in formal or legal settings.
契約書に署名するときは、立会人が必要です。
When signing a contract, a witness is required.
試験
The exam observer monitors for any cheating.
目撃者 is an eyewitness to an incident, often accidental or criminal, whereas 立会人 is an official or designated observer present by arrangement.
Compound of 立ち会い (tachiai, 'attendance, presence') + 人 (nin, 'person'). The kanji 立会 means 'to be present at', and 人 denotes the person performing the action.