'hyleg' likely originates from Arabic, specifically the word 'haylaj' (recorded in medieval astrological texts), where the root conveyed the idea of a life‑giving principle.

'hyleg' entered medieval Latin and Middle English astrological vocabulary from Arabic sources and was used in technical astrological works in the Middle Ages and Renaissance before becoming a rare specialist term in modern English.

Initially it referred specifically to the astrological 'giver of life' in natal and genethliacal astrology; that technical meaning has largely been preserved, though the term is now rare and chiefly historical/technical.