Definition of diminutive noun from the Oxford Advanced Learner's Dictionary

diminutive

noun
dɪˈmɪnjətɪv
 
; dɪˈmɪnjətɪv
 
 
1 a word or an ending of a word that shows that somebody/something is small, for example piglet(= a young pig), kitchenette(= a small kitchen)2 a short informal form of a word, especially a name‘Nick’ is a common diminutive of ‘Nicholas’.