Thomasin is an English feminine form of Thomas, from Aramaic via Hebrew tradition, meaning "twin."
Thomasin is the old English feminine form of Thomas, a name of Aramaic origin meaning 'twin.' Thomas entered Western culture through the New Testament apostle Thomas — famously called Didymus, the Greek word also meaning 'twin' — whose honest doubt and eventual faith made him one of the most humanly compelling figures in Christian scripture. The name became enormously popular in medieval England, boosted by the cult of Saint Thomas Becket, the Archbishop of Canterbury martyred in 1170.
Thomasin arose as a natural feminization, common in England from the medieval period through the eighteenth century. The name received one of its finest literary moments in Thomas Hardy's 1878 novel The Return of the Native, where Thomasin Yeobright is among the novel's most sympathetic characters — gentle, clear-eyed, and morally grounded against a backdrop of passion and destruction on Egdon Heath. Hardy's use of the name was deliberately archaic, evoking the deep rural Dorset culture he was chronicling.
More recently, the name gained a striking new association through Robert Eggers' 2015 folk horror film The Witch, where the protagonist Thomasin is a Puritan girl whose fierce spiritual intelligence drives the narrative. This dual literary legacy — Hardy's warmth and Eggers' intensity — gives Thomasin an unusually rich modern resonance. It has attracted renewed interest among parents drawn to genuinely historical names that feel neither fusty nor manufactured, and it wears its centuries of use with quiet grace.