hypocoristic:

From Ancient Greek ?ποκοριστικ?? ?(hupokoristikós), from ?ποκορ?ζομαι ?(hupokorízomai, “I speak in the language of children”), from ?π? ?(hupó, “below”) + κορ?ζομαι ?(korízomai, “I act like a girl”), from κ?ρη ?(kórē, “girl”).