lamb roast vs roast

lamb roast and roast both are nouns.

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

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

lamb roast: a cut of lamb 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 lamb roast include joint.

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

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

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