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hypocorism: (hi - pock - uh - rizz - um) noun 1. A name of endearment; a pet name. 2. The use of such names. Other forms: hypocoristic (adjective), hypocoristically (adverb).
Etymology: late Latin hypocorisma, from Greek hupokorisma, from hupokorizesthai - to call by endearing names: hypo-, beneath, secretly; korizesthai, to caress.
Source: The American heritage Dictionary of the English Language, fourth edition (2000).