Jillaine / Gillian / Juliana

Jillaine is a relatively modern name, likely a variant or elaboration of Jill. The name Jill itself originated as a diminutive of Gillian, which is the medieval English form of Juliana. Juliana is derived from the Roman family name Julianus, meaning 'of the gens Iulia' or 'descended from Julius'. The name Julius is thought to be derived from the Greek 'ioulos', meaning 'downy-bearded' or 'youthful'.

The 'aine' suffix in Jillaine is a common French diminutive or feminine ending, suggesting a possible French influence or a desire to create a more elaborate and distinctive feminine form. While Jill and Gillian have long histories, Jillaine appears to be a more recent coinage, gaining some usage in the 20th century.