Different Functions of That
I know the basic functions of that: relative pronoun, demonstrative pronoun, demonstrative adjective, etc. However, I have heard people use, myself included, that as a word to place emphasis on an adjective. Ex "I'm not THAT smart" or "It's not THAT good." So can "that" also be used as an adverb since it gives more meaning to an adjective? iIs it an unofficial use of the word? Or, finally, is it somehow an demonstrative adjective, referring to the idea of being something?
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