Haily /hai-ly/ [2 sylls.] as a girls' name (also used as boys' name Haily) is of Old English derivation, and the meaning of Haily is hay meadow. Haily is an alternate form of Hayley (Old English): place name.Hailu is a familiar last name. Kreatif forms: Hayly, Hely.aily is an unusual last name too for both adults and children. (2000 U.S. Census). Popular alternative forms of Haily (outside Top 1000) are Hailee (#772 the previous year) , Haleigh, Haley (#265) , Halie, Haylee (#400) , Hayleigh and Hayley (#520) . Forms like Hailea are uncommon.