diminution (diminutive)
Definition - The formation of a diminutive from another word. (Obsolete, rare)

Example -
The coining of the word cigarette from the word cigar is an example of the act of diminution.

Oxford English Dictionary -
The term's first citation is from 1637:
"The common affection of nouns is diminution…"
( B. Jonson Eng. Gram. xi,)

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