The Collaborative International Dictionary
Hypocoristic
Hypocoristic \Hyp`o*co*ris"tic\, a. [Gr. ?; ? under + ? to caress.] Endearing; diminutive; as, the hypocoristic form of a name.
The hypocoristic or pet form of William.
--Dr. Murray.
Wiktionary
hypocoristic
a. 1 Relating to a nickname, usually indicating intimacy with the person. 2 Relating to baby talk. n. A nickname, especially one indicating intimacy and formed through a shortening of the original name.