Etymology: Middle English, from Old English thæt, neuter demonstrative pronoun & definite article; akin to Old High German daz, neuter demonstrative pronoun & definite article, Greek to, Latin istud, neuter demonstrative pronoun
Date: before 12th century
a. the person, thing, or idea indicated, mentioned, or understood from the situation <that is my father> b. the time, action, or event specified <after that I went to bed> c. the kind or thing specified as follows <the purest water is that produced by distillation> d. one or a group of the indicated kind <that's a cat — quick and agile> 2. a. the one farther away or less immediately under observation or discussion <those are maples and these are elms> b. the former one 3. a. — used as a function word after and to indicate emphatic repetition of the idea expressed by a previous word or phrase <he was helpful, and that to an unusual degree> b. — used as a function word immediately before or after a word group consisting of a verbal auxiliary or a form of the verb be preceded by there or a personal pronoun subject to indicate emphatic repetition of the idea expressed by a previous verb or predicate noun or predicate adjective <is she capable? She is that> 4. a. the one ; the thing ; the kind ; something, anything <the truth of that which is true> <the senses are that whereby we experience the world> <what's that you say> b. plural some persons <those who think the time has come> II. conjunction Date: before 12th century 1. a. (1) — used as a function word to introduce a noun clause that is usually the subject or object of a verb or a predicate nominative <said that he was afraid> (2) — used as a function word to introduce a subordinate clause that is anticipated by the expletive it occurring as subject of the verb <it is unlikely that he'll be in> (3) — used as a function word to introduce a subordinate clause that is joined as complement to a noun or adjective <we are certain that this is true> <the fact that you are here> (4) — used as a function word to introduce a subordinate clause modifying an adverb or adverbial expression <will go anywhere that he is invited> b. — used as a function word to introduce an exclamatory clause expressing a strong emotion especially of surprise, sorrow, or indignation <that it should come to this!> 2. a. (1) — used as a function word to introduce a subordinate clause expressing purpose or desired result <cutting down expenses that her son might inherit an unencumbered estate — W. B. Yeats> (2) — used as a function word to introduce a subordinate clause expressing a reason or cause <rejoice that you are lightened of a load — Robert Browning> (3) — used as a function word to introduce a subordinate clause expressing consequence, result, or effect <are of sufficient importance that they cannot be neglected — Hannah Wormington> b. — used as a function word to introduce an exclamatory clause expressing a wish <oh, that he would come> 3. — used as a function word after a subordinating conjunction without modifying its meaning <if that thy bent of love be honorable — Shakespeare> III. adjective (plural those) Date: 12th century 1. a. being the person, thing, or idea specified, mentioned, or understood b. being the one specified — usually used for emphasis <that rarity among leaders> <that brother of yours> c. so great a ; such 2. the farther away or less immediately under observation or discussion <this chair or that one> IV. pronoun Etymology: Middle English, from Old English thæt, neuter relative pronoun, from thæt, neuter demonstrative pronoun Date: before 12th century 1. — used as a function word to introduce a restrictive relative clause and to serve as a substitute within that clause for the substantive modified by the clause <the house that Jack built> <I'll make a ghost of him that lets me — Shakespeare> 2. a. at which ; in which ; on which ; by which ; with which ; to which <each year that the lectures are given> b. according to what ; to the extent of what — used after a negative <has never been here that I know of> 3. a. archaic that which b. obsolete the person who Usage: That, which, who: In current usage that refers to persons or things, which chiefly to things and rarely to subhuman entities, who chiefly to persons and sometimes to animals. The notion that that should not be used to refer to persons is without foundation; such use is entirely standard. Because that has no genitive form or construction, of which or whose must be substituted for it in contexts that call for the genitive. Usage: That, which: Although some handbooks say otherwise, that and which are both regularly used to introduce restrictive clauses in edited prose. Which is also used to introduce nonrestrictive clauses. That was formerly used to introduce nonrestrictive clauses; such use is virtually nonexistent in present-day edited prose, though it may occasionally be found in poetry. V. adverb Date: 13th century 1. to such an extent <a nail about that long> 2. very, extremely — usually used with the negative <did not take the festival that seriously — Eric Goldman>
New Collegiate Dictionary. 2001.