hypocorism

noun3

1. •
   A term of endearment, often a diminutive; a pet name.

   • For the flattering hypocorisms of lovers and parents see Plut. de Leg. Poet. p. 44; [...] — 1865
2. •
   The formation of terms of endearment or pet names.

   • St Peter's cult, which dates from the earliest period in Brittany, is represented in the toponymy only in the radical form of his name, without hypocorism or mutation. — 2000
3. •
   (rare) Baby talk, such as bow-wow for dog and choo-choo for train.

   • In European languages reduplication is often associated with hypocorism or baby talk (e.g. wee-wee, or French bonbon) but this is not the case in the Atlantic creoles and the Niger-Congo languages. — 1988