work permit vs legal instrument

work permit and legal instrument both are nouns.

Word	Noun	Adjective	Verb	Adverb
work permit	Yes	No	No	No
legal instrument	Yes	No	No	No

As nouns, legal instrument is a hypernym of work permit; that is, legal instrument is a word with a broader meaning than work permit:

work permit: a legal document giving information required for employment of certain people in certain countries
legal instrument: (law) a document that states some contractual relationship or grants some right

Other hypernyms of work permit include instrument, legal document, official document.

work permit (noun)	legal instrument (noun)
a legal document giving information required for employment of certain people in certain countries	(law) a document that states some contractual relationship or grants some right