Etymology
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convex (adj.)

"curved like a circle or sphere when viewed from outside," 1570s, from French convexe, from Latin convexus "vaulted, arched," past participle of convehere "to bring together," from assimilated form of com "with, together," or "thoroughly" (see com-) + vehere "to bring, carry, convey" (from PIE root *wegh- "to go, move, transport in a vehicle").

Possibly the notion is of vaults "carried together" to meet at the point of a roof. Related: Convexity. Convex lens is from 1822.

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*wegh- 

Proto-Indo-European root meaning "to go, move, transport in a vehicle."

The root wegh-, "to convey, especially by wheeled vehicle," is found in virtually every branch of Indo-European, including now Anatolian. The root, as well as other widely represented roots such as aks- and nobh-, attests to the presence of the wheel — and vehicles using it — at the time Proto-Indo-European was spoken. [Watkins, p. 96]

It forms all or part of: always; away; convection; convey; convex; convoy; deviate; devious; envoy; evection; earwig; foy; graywacke; impervious; invective; inveigh; invoice; Norway; obviate; obvious; ochlocracy; ogee; pervious; previous; provection; quadrivium; thalweg; trivia; trivial; trivium; vector; vehemence; vehement; vehicle; vex; via; viaduct; viatic; viaticum; vogue; voyage; wacke; wag; waggish; wagon; wain; wall-eyed; wave (n.); way; wee; weigh; weight; wey; wiggle.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit vahati "carries, conveys," vahitram, vahanam "vessel, ship;" Avestan vazaiti "he leads, draws;" Greek okhos "carriage, chariot;" Latin vehere "to carry, convey," vehiculum "carriage, chariot;" Old Church Slavonic vesti "to carry, convey," vozŭ "carriage, chariot;" Russian povozka "small sled;" Lithuanian vežu, vežti "to carry, convey," važis "a small sled;" Old Irish fecht "campaign, journey," fen "carriage, cart;" Welsh gwain "carriage, cart;" Old English wegan "to carry;" Old Norse vegr, Old High German weg "way;" Middle Dutch wagen "wagon."

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lenticular (adj.)
"lens-shaped, having the form of a double-convex lens," early 15c., from Late Latin lenticularis "lentil-shaped," from lenticula "a small lentil," diminutive of Latin lens "a lentil" (see lentil). Related: Lenticularity (1890).
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meniscus (n.)

"a crescent or crescent-shaped body," 1690s in reference to lenses convex on one side, concave on the other, and thicker in the middle; c. 1812 in reference to liquid surfaces, Modern Latin meniscus, from Greek meniskos "lunar crescent," diminutive of mene "moon" (see moon (n.)). Related: Meniscoid; mensicoidal; mensical; mensicate.

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lens (n.)

1690s, "glass to regulate light rays," from Latin lens (genitive lentis) "a lentil," on analogy of the double-convex shape. See lentil. Anatomical use, of the eye part, from 1719. Lens-cap is from 1857.

In the vernacular of the photographer, anyone crowding to the front of a group, staring into the lens, or otherwise attracting attention to himself is known as a "lens louse." ["American Photography," vol. xl, 1946; the term dates from 1915]
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scallop (v.)

1737 in cookery, "to bake or brown with sauce in a scallop-shell-shaped pan," by 1737, from scallop (n.); originally of oysters and the notion might have been baking or serving them in a large scallop shell. Related: Scalloped "cooked in a scallop-pan;" also "with the edges marked or cut into convex rounded lobes;" scalloping

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gibbous (adj.)

c. 1400, "bulging, convex," from Late Latin gibbus "hunchbacked," from Latin gibbus "a hump, a hunch," as an adjective, "bulging," from Proto-Italic *gifri- "hump," *gifro- "hump-backed," of uncertain origin. De Vaan suggests a PIE *geibh-, with possible cognates in Lithuanian geibus "gawky, plump," geibstu, geibti "become weak;" Norwegian dialect keiv "slanted, wrong," keiva "left hand," perhaps united by a general sense of "bodily defect." Of the moon from early 15c.; also used from 15c. of hunchbacks. Related: Gibbosity.

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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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