roast beef vs roast

roast beef and roast both are nouns.

Word	Noun	Adjective	Verb	Adverb
roast beef	Yes	No	No	No
roast	Yes	Yes	Yes	No

As nouns, roast is a hypernym of roast beef; that is, roast is a word with a broader meaning than roast beef:

roast beef: cut of beef suitable for roasting
roast: a piece of meat roasted or for roasting and of a size for slicing into more than one portion

Other hypernyms of roast beef include joint.

roast beef (noun)	roast (noun)
cut of beef suitable for roasting	negative criticism
	a piece of meat roasted or for roasting and of a size for slicing into more than one portion

roast beef (adjective)	roast (adjective)
	(meat) cooked by dry heat in an oven

roast beef (verb)	roast (verb)
	cook with dry heat, usually in an oven
	subject to laughter or ridicule