The story
- Old English · derived frombī healfe“by [his/her] side”
- Middle English · derived frombihalve“nearby”
- English todaybehalf
From Middle English bihalve (“nearby”), from Old English bī healfe (“by [his/her] side”), from bī (“by”) + healfe (“side, half”), equivalent to be- + half.
Etymology from Wiktionary, CC BY-SA 4.0.