Likely influenced by Vanessa and Manasseh; it is a modern form with possible Hebrew echo meaning causing to forget.
Manessa appears to be a feminine elaboration drawing on the ancient Hebrew name Manasseh, one of the great patriarchal names of the Old Testament. Manasseh — from the Hebrew Menashsheh, meaning "causing to forget" or "one who makes forgetful" — was the name given by Joseph to his firstborn son in Egypt, a name that encoded his entire emotional journey: God had made him forget all his hardship and all his father's house. The tribe of Manasseh became one of the Twelve Tribes of Israel, giving the name enormous theological and historical weight across Jewish, Christian, and Islamic traditions.
Manasseh also appears as the name of one of Judah's most controversial kings, who reigned for fifty-five years — longer than any other king of Judah — and whose legacy in the Hebrew Bible is one of moral complexity: a king who promoted idolatry but who, according to the Books of Chronicles, later repented and reformed. This complicated story gave the name a gravitas that simple virtue names rarely carry. Manassa, an American variant, appears in history as the birthplace of Jack Dempsey, the heavyweight boxing champion, and the name Manassa itself derives from the same biblical root.
Manessa as a feminine form is a modern English-language creation, following a long tradition of feminizing biblical male names — much as Joshua became Josephine, or Daniel became Danielle. The soft "-essa" ending adds a romance-language lilt that balances the name's biblical solidity with something flowing and contemporary. Parents choosing Manessa today often discover its etymology later, finding that the ancient story of forgiveness and renewal gives the name unexpected emotional depth.