though adv., conj.

Old English þæt, "that, so that, after that," neuter singular demonstrative pronoun ("A Man's a Man for a' that"), relative pronoun ("O thou that hearest prayer"), and demonstrative adjective ("Look at that caveman go!"), corresponding to masc. se, fem. seo. From Proto-Germanic *that, from PIE *tod-, extended form of demonstrative pronominal base *-to- (see -th (1)).

With the breakdown of the grammatical gender system, it came to be used in Middle English and Modern English for all genders. Germanic cognates include Old Saxon that, Old Frisian thet, Middle Dutch, Dutch dat "that," German der, die, das "the."

Generally more specific or emphatic than the, but in some cases they are interchangeable. From c. 1200 opposed to this as indicating something farther off. In adverbial use ("I'm that old"), in reference to something implied or previously said, c. 1200, an abbreviation of the notion of "to that extent," "to that degree." As a conjunction ("Not that I loved Caesar less, but that I loved Rome more") it was originally the neuter pronoun or adjective that used practically as a definite article qualifying the whole sentence.

Slang that way "in love" first recorded 1929. That-a-way "in that direction" is recorded from 1839. "Take that!" said while delivering a blow, is recorded from early 15c.

late 14c., from Old English (Anglian) hlæhhan, earlier hliehhan, hlihhan "to laugh, laugh at; rejoice; deride," from Proto-Germanic *klakhjan (source also of Old Norse hlæja, Danish le, Old Frisian hlakkia, Old Saxon hlahhian, Middle Dutch and Dutch lachen, Old High German hlahhan, German lachen, Gothic hlahjan), from PIE *kleg-, of imitative origin (compare Latin cachinnare "to laugh aloud," Sanskrit kakhati "laughs," Old Church Slavonic chochotati "laugh," Lithuanian klagėti "to cackle," Greek kakhazein).

Originally with a "hard" -gh- sound, as in Scottish loch; the spelling remained after the pronunciation shifted to "-f."

If laugh were written as it is pronounced, laaff, there would be nothing in the word itself to put us in mind of the thing signified. The imitation begins to be felt in the guttural ach of G. lachen, and is clearly indicated in the reduplicate form of the Du. lachachen, to hawhaw or laugh loud, preserved by Kilian. [Hensleigh Wedgwood, introduction to "A Dictionary of English Etymology," 1878] 

To laugh in one's sleeve is to laugh inwardly so as not to be observed:

If I coveted nowe to avenge the injuries that you have done me, I myght laughe in my slyve. [John Daus, "Sleidanes Commentaries," 1560]

"The phrase generally implies some degree of contempt, and is used rather of a state of feeling than of actual laughter" [Century Dictionary]. Related: Laughed; laugher; laughing.