that

from The Century Dictionary.

• Introducing a reason: in that; because.
• Introducing an object or final end or purpose: equivalent to the phrases in order that, for the purpose that, to the effect that.
• Introducing a result or consequence.
• Introducing a clause as the subject or object of the principal verb, or as a necessary complement to a statement made.
• Seeing; since; inasmuch as.
• Formerly often used after a preposition, introducing a noun-clause as the object of the preposition: as, before that he came, after that they had gone, etc., where at present the that is omitted and the preposition has become a conjunction; also, by mistaken analogy with such cases, that was occasionally added after real conjunctions, as when that, where that.
• Sometimes used in place of another conjunction, in repetition.
• Used elliptically to introduce a sentence or clause expressive of surprise, indignation, or some kindred emotion.
• Used as an optative particle, or to introduce a phrase expressing a wish: would that: usually with O!
• Used as a definitive adjective before a noun, in various senses.
• Frequently in opposition to this, in which case it refers to one of two objects already mentioned, and often to the one more distant in place or time: frequently, however, mere contradistinction is implied: as, I will take this book, and you can take that one.
• Pointing not so much to persons and things as to their qualities, almost equivalent to such, or of such a nature, and occasionally followed by as or that as a correlative.
• Used absolutely or without a noun as a demonstrative pronoun.
• In opposition to this, or by way of distinction.
• When this and that refer to foregoing words, this, like the Latin hic or the French ceci, refers to the last mentioned, the latter, and that, like the Latin ille or the French cela, to the first mentioned, the former.
• In all the above cases, that, when referring to a plural noun, takes the plural form those: as, that man, those men; give me that, give me those; and so on.
• To represent a sentence or part of a sentence, or a series of sentences.
• That sometimes in this use precedes the sentence or clause to which it refers.
• That here represents the clause in italics. It is used also as the substitute for an adjective: as, you allege that the man is innocent; that he is not. Similarly, it is often used to introduce an explanation of something going before: as, “religion consists in living up to those principles—that is, in acting in conformity to them.”
• Emphatically, in phrases expressive of approbation, applause, or encouragement.
• As the antecedent of a relative: as, that which was spoken.
• By the omission of the relative, that formerly sometimes acquired the force of what or that which.
• With of, to avoid repetition of a preceding noun: as, his opinions and those of the others.
• With and, to avoid repetition of a preceding statement.
• Used for who or which.
• In the following extract that, who, and which are used without any perceptible difference.
• With the use of that as a relative are to be classed those cases in which it is used as a correlative to so or such.
• That as a demonstrative and that as a relative pronoun sometimes occur close together, but this use is now hardly approved.
• Frequently used in Chaucer for the definite article, before one or other, usually when the two words are put in contrast.
• That … he = who; that … his (or her) = whose; that … him = whom; that … they = who; which that = whom.
• To that extent; to that degree; to such a degree; so: as, I did not go that far; I did not care that much about it: the comparison being with something previously said or implied, as in the preceding examples: used colloquially to express emphasis.

from the GNU version of the Collaborative International Dictionary of English.

• As a demonstrative pronoun (pl. those), that usually points out, or refers to, a person or thing previously mentioned, or supposed to be understood. That, as a demonstrative, may precede the noun to which it refers
• As an adjective, that has the same demonstrative force as the pronoun, but is followed by a noun.
• As a relative pronoun, that is equivalent to who or which, serving to point out, and make definite, a person or thing spoken of, or alluded to, before, and may be either singular or plural.
• As a conjunction, that retains much of its force as a demonstrative pronoun.
• To introduce a clause employed as the object of the preceding verb, or as the subject or predicate nominative of a verb.
• To introduce, a reason or cause; -- equivalent to for that, in that, for the reason that, because.
• To introduce a purpose; -- usually followed by may, or might, and frequently preceded by so, in order, to the end, etc.
• To introduce a consequence, result, or effect; -- usually preceded by so or such, sometimes by that.
• In an elliptical sentence to introduce a dependent sentence expressing a wish, or a cause of surprise, indignation, or the like.
• Archaic or in illiteral use. As adverb: To such a degree; so.
• everything of that kind; all that sort.
• See under For, prep.
• See under In, prep.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• determiner The (thing) being indicated (at a distance from the speaker, or previously mentioned, or at another time).
• pronoun demonstrative That aforementioned quality.
• adverb degree To a given extent or degree; particularly.
• adverb standard in negative constructions So, so much; very.
• noun philosophy Something being indicated that is there; one of those.