armchair (n.)youdaoicibaDictYouDict[armchair 词源字典]
also arm-chair, 1630s, from arm (n.1) + chair; adjective sense in reference to "criticism of matters in which the critic takes no active part" is from 1886. Another old name for it was elbow-chair (1650s).[armchair etymology, armchair origin, 英语词源]