taxation vs gift tax

taxation and gift tax both are nouns.

Word	Noun	Adjective	Verb	Adverb
taxation	Yes	No	No	No
gift tax	Yes	No	No	No

As nouns, gift tax is a hyponym of taxation; that is, gift tax is a word with a more specific, narrower meaning than taxation:

taxation: charge against a citizen's person or property or activity for the support of government
gift tax: a tax imposed on transfers of property by gift during the lifetime of the giver

taxation (noun)	gift tax (noun)
the imposition of taxes; the practice of the government in levying taxes on the subjects of a state	a tax imposed on transfers of property by gift during the lifetime of the giver
charge against a citizen's person or property or activity for the support of government
government income due to taxation