English form of Juliana, ultimately from the Roman family name Julius.
Gillian is the medieval English feminine form of Julian, itself derived from the Roman family name Julius — a name whose origins may reach back to the mythological Iulus, son of Aeneas, or possibly to a pre-Latin root meaning "downy-bearded" (referring to youthful first growth). The name Julius was borne by the greatest of Roman generals and statesmen, but it was through the Christian calendar — particularly through Saint Juliana of Nicomedia, martyred in the early fourth century — that the feminine Julian entered popular use in England. Over centuries of spoken English, Julian softened and shifted into Gillian, with its characteristic hard G replacing the original J.
In medieval England, Gillian was so common that "Jill" (its diminutive) became a byword for any ordinary woman, as in the proverb "Every Jack has his Jill." The name appears in nursery rhymes, folk songs, and the everyday texture of medieval English life. It belonged to the merchant classes and the aristocracy alike, a true cross-strata name.
After centuries of relative dormancy, Gillian staged a significant revival in twentieth-century Britain, where it reached peak popularity in the 1950s and 60s, carried by actresses, novelists, and the general post-war enthusiasm for names with English historical depth. In North America, Gillian remained somewhat rarer, giving it a pleasantly Anglo quality to American ears. The X-Files actress Gillian Anderson, whose long-running role as the skeptical, brilliant Dana Scully made her a cultural touchstone for a generation, gave the name a sharp, intelligent edge in the 1990s. Today Gillian sits comfortably in the vintage-revival category: rooted, melodious, and far more interesting than its more common cousin Jillian.