tax return vs legal document

tax return and legal document both are nouns.

Word	Noun	Adjective	Verb	Adverb
tax return	Yes	No	No	No
legal document	Yes	No	No	No

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

tax return: document giving the tax collector information about the taxpayer's tax liability
legal document: (law) a document that states some contractual relationship or grants some right

Other hypernyms of tax return include instrument, legal instrument, official document.

tax return (noun)	legal document (noun)
document giving the tax collector information about the taxpayer's tax liability	(law) a document that states some contractual relationship or grants some right