tax bracket vs bracket

tax bracket and bracket both are nouns.

Word	Noun	Adjective	Verb	Adverb
tax bracket	Yes	No	No	No
bracket	Yes	No	Yes	No

As nouns, bracket is a hypernym of tax bracket; that is, bracket is a word with a broader meaning than tax bracket:

tax bracket (noun)	bracket (noun)
a category of taxpayers based on the amount of their income	a support projecting from a wall (as to hold a shelf)
	either of two punctuation marks ([ or ]) used to enclose textual material
	either of two punctuation marks (`<' or `>') used in computer programming and sometimes used to enclose textual material
	a category falling within certain defined limits