kitty vs pussycat

kitty and pussycat both are nouns.

Word	Noun	Adjective	Verb	Adverb
kitty	Yes	No	No	No
pussycat	Yes	No	No	No

As nouns, kitty and pussycat are synonyms defined as:

Other synonyms of kitty include kitty-cat, puss, pussy.

kitty (noun)	pussycat (noun)
informal terms referring to a domestic cat	informal terms referring to a domestic cat
young domestic cat	a person who is regarded as easygoing and agreeable
the combined stakes of the betters
the cumulative amount involved in a game (such as poker)