taxicab vs gypsy cab

taxicab and gypsy cab both are nouns.

Word	Noun	Adjective	Verb	Adverb
taxicab	Yes	No	No	No
gypsy cab	Yes	No	No	No

As nouns, gypsy cab is a hyponym of taxicab; that is, gypsy cab is a word with a more specific, narrower meaning than taxicab:

taxicab: a car driven by a person whose job is to take passengers where they want to go in exchange for money
gypsy cab: a taxicab that cruises for customers although it is licensed only to respond to calls

Other hyponyms of taxicab include minicab.

taxicab (noun)	gypsy cab (noun)
a car driven by a person whose job is to take passengers where they want to go in exchange for money	a taxicab that cruises for customers although it is licensed only to respond to calls