Etymology
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belly (n.)

a general Germanic word for "leather bag, pouch, pod" that in English has evolved to mean a part of the body; from Old English belg, bylig (West Saxon), bælg (Anglian) "leather bag, purse, pouch, pod, husk, bellows," from Proto-Germanic *balgiz "bag" (source also of Old Norse belgr "bag, bellows," bylgja "billow," Gothic balgs "wine-skin"), from PIE *bhelgh- "to swell," extended form of root *bhel- (2) "to blow, swell."

By c. 1200 it was being used for "the stomach," especially as a symbol of gluttony, and by late 14c. to mean "abdomen of a human or animal, front part of the body between the breast and the groin or the diaphragm and the pelvis."

The Old English word for "belly, stomach" was buc (cognate with German Bauch, Dutch buik, Old Frisian buk, from West Germanic *būkaz, a word indicative of swelling, with no known connections). The plural of Old English belg emerged in Middle English as a separate word, bellows. Meaning "bulging part or convex surface of anything" is 1590s. The West Germanic root had a figurative or extended sense of "anger, arrogance" (as in Old English bolgenmod "enraged;" belgan (v.) "to become angry"), probably from the notion of "swelling."

Indo-European languages commonly use the same word for both the external belly and the internal (stomach, womb, etc.), but the distinction of external and internal is somewhat present in English belly/stomach; Greek gastr- (see gastric) in classical language denoted the paunch or belly, while modern science uses it only in reference to the stomach as an organ.

As a personal name from 12c. Belly-naked in Middle English was "stripped to the belly, completely naked." Fastidious avoidance of belly in speech and writing (compensated for by stretching the senses of imported stomach and abdomen, baby-talk tummy and misappropriated midriff) began late 18c. and the word was banished from Bibles in many early 19c. editions.

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belly (v.)
c. 1600 "cause to swell out;" 1620s, "to swell out" (intrans.), from belly (n.). Related: Bellied; bellying. Old English belgan meant "to be or become angry" (a figurative sense). A comparable Greek verb-from-noun, gastrizein, meant "to hit (someone) in the belly."
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laugh (n.)
1680s, "action of laughing," from laugh (v.). The older noun form is laughter. Meaning "a cause of laughter" is from 1895; ironic use (in that's a laugh) attested from 1930. Laugh track "pre-recorded laughter on a TV program" is from 1961.
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laugh (v.)

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.

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belly-ache (n.)
also bellyache, 1590s, "pain in the bowels," from belly (n.) + ache (n.). The verb in the slang sense of "complain" is first recorded 1888, American English; it appears not to have been used earlier than that, if ever, in a literal sense. Related: bellyached; bellyaching.
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pot-belly (n.)

"a protuberant belly; a person having a protuberant belly," 1714, from pot (n.1) + belly (n.). Pot-belly stove, so called for its shape, attested from 1940.

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belly-dance (n.)

also bellydance, 1883, in a British account of travels in Persia, from belly (n.) + dance (n.). In early use sometimes referred to by the French danse du ventre, which is attested by 1872 in French accounts from the Middle East. It appears as a French term in English by 1883, and its use got a boost from the performances of it at the Paris Exposition of 1889.

We agreed, and made our way to the mimic street called Grand Cairo, where we witnessed the lady contortionist who performs a series of movements, designated with charming frankness on the affiches as "La Danse du Ventre." It might with equal candor be called the Lumbar Wriggle [or] the Pectoral Squirm, for this curious Arab almeh possesses the power of moving any one of her principal sets of muscles quite independently of all the others, and can make any prominent part of her person waggle or surge, while its neighboring lines or curves preserve a statuesque rigidity. [Table Talk, September 1889]
The number of women [in the audience] was ludicrously disproportionate, and the number of American women was noticeable. Some of them seemed slightly pensive, but all were interested. Their large eyes grew larger still. They almost forgot decorum in crowding for a better view, in leaning over the backs of chairs in concentrated absorbed attention. [Scribner's Magazine, January 1890]

The English noun is perhaps a direct translation of the French. As a verb from 1963. Related: Belly-dancer (1922); belly-dancing (n.), 1921.

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belly-punch (n.)
also bellypunch, "fist-blow to the stomach," 1811, from belly (n.) + punch (n.3).
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belly-button (n.)
also bellybutton, "navel," 1877, colloquial, from belly (n.) + button (n.).
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labonza (n.)
"belly," 1943, American English slang, probably from dialectal pronunciation of Italian la pancia "the belly," with the definite article absorbed, from Latin pantex (genitive panticis) "belly" (see paunch).
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