Great and Grate
Great can mean "really good." Note that it is an adjective, not an adverb. You can say that Susan is a great player, or that she played a great game. You cannot, however, say that "Susan played great." Great can only modify nouns.
"Great" can also mean that something is one level up in a hierarchy. My great-grandfather is the grandfather of my father. The greater Toronto area is the area around Toronto, containing Toronto.
Grate can be a noun describing something with a grid structure, or a verb to describe shredding something.