roast vs top round

roast and top round both are nouns.

Word	Noun	Adjective	Verb	Adverb
roast	Yes	Yes	Yes	No
top round	Yes	No	No	No

As nouns, top round is a hyponym of roast; that is, top round is a word with a more specific, narrower meaning than roast:

roast: a piece of meat roasted or for roasting and of a size for slicing into more than one portion
top round: roast cut from the round; usually suitable for roasting

roast (noun)	top round (noun)
negative criticism	roast cut from the round; usually suitable for roasting
a piece of meat roasted or for roasting and of a size for slicing into more than one portion

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

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