Left person radical — the side-form of
人. The indexing radical, marking
侍 as a person-doing-X verb: to attend, wait upon, serve a superior. Same radical groups
侍 with
仆 (servant),
伴 (companion),
侯 (marquis),
侯 (wait) — many of the social-role terms in classical Chinese sit here. A subordinate figure standing in attendance.