1. (used to indicate a person, thing, idea, state, event, time, remark, etc., as pointed out or present, mentioned before, supposed to be understood, or by way of emphasis): That is her mother. After that we saw each other.
2. (used to indicate one of two or more persons, things, etc., already mentioned, referring to the one more remote in place, time, or thought; opposed to this): This is my sister and that's my cousin.
3. (used to indicate one of two or more persons, things, etc., already mentioned, implying a contrast or contradistinction; opposed to this): This suit fits better than that.
4. (used as the subject or object of a relative clause, esp. one defining or restricting the antecedent, sometimes replaceable by who, whom, or which): the horse that he bought.
5. (used as the object of a preposition, with the preposition standing at the end of a relative clause): the farm that I spoke of.
6. (used in various special or elliptical constructions): fool that he is.
7. (used to indicate a person, place, thing, or degree as indicated, mentioned before, present, or as well-known or characteristic): That woman is her mother. Those little mannerisms of hers make me sick.
8. (used to indicate the more remote in time, place, or thought of two persons, things, etc., already mentioned; opposed to this): This room is his and that one is mine.
9. (used to imply mere contradistinction; opposed to this): not this house, but that one.
10. (used with adjectives and adverbs of quantity or extent) to the extent or degree indicated: that much; The fish was that big.
11. to a great extent or degree; very: It's not that important.
12. Dialect. (used to modify an adjective or another adverb) to such an extent: He was that weak he could hardly stand.