Jill Look up Jill at Dictionary.com
fem. proper name, Middle English Jille, Jylle, Gille, etc., familiar shortening of Jillian, Gillian, which represent the common Middle English pronunciation of Juliana (see Gillian). A very popular name for girls in medieval England, hence its use as a familiar, almost generic, name for a girl (early 15c.; paired with Jack since mid-15c.).