city slicker vs city boy

city slicker and city boy both are nouns.

Word	Noun	Adjective	Verb	Adverb
city slicker	Yes	No	No	No
city boy	Yes	No	No	No

As nouns, city slicker and city boy are synonyms defined as:

city slicker and city boy: a city dweller with sophisticated manners and clothing

city slicker (noun)	city boy (noun)
a city dweller with sophisticated manners and clothing	a city dweller with sophisticated manners and clothing