Etymology
Advertisement
billow (n.)
"a great wave or surge of the sea," 1550s, perhaps older in dialectal use (but not recorded in Middle English), from Old Norse bylgja "a wave, a billow," from Proto-Germanic *bulgjan (source also of Swedish bölja, Danish bölge "a billow," Middle High German bulge "a billow; a bag"), from PIE *bhelgh- "to swell," extended form of root *bhel- (2) "to blow, swell."
Related entries & more 
Advertisement
billow (v.)
"to rise or roll in large waves," 1590s, from billow (n.). Related: Billowed; billowing.
Related entries & more 
billowy (adj.)
1610s, from billow (n.) + -y (2). Related: Billowiness.
Related entries & more 
*bhel- (2)
Proto-Indo-European root meaning "to blow, swell," "with derivatives referring to various round objects and to the notion of tumescent masculinity" [Watkins].

It forms all or part of: bale (n.) "large bundle or package of merchandise prepared for transportation;" baleen; ball (n.1) "round object, compact spherical body;" balloon; ballot; bawd; bold; bole; boll; bollocks; bollix; boulder; boulevard; bowl (n.) "round pot or cup;" bulk; bull (n.1) "bovine male animal;" bullock; bulwark; follicle; folly; fool; foosball; full (v.) "to tread or beat cloth to cleanse or thicken it;" ithyphallic; pall-mall; phallus.

It is the hypothetical source of/evidence for its existence is provided by: Greek phyllon "leaf," phallos "swollen penis;" Latin flos "flower," florere "to blossom, flourish," folium "leaf;" Old Prussian balsinis "cushion;" Old Norse belgr "bag, bellows;" Old English bolla "pot, cup, bowl;" Old Irish bolgaim "I swell," blath "blossom, flower," bolach "pimple," bolg "bag;" Breton bolc'h "flax pod;" Serbian buljiti "to stare, be bug-eyed;" Serbo-Croatian blazina "pillow."

An extended form of the root, *bhelgh- "to swell," forms all or part of: bellows; belly; bilge; billow; bolster; budget; bulge; Excalibur; Firbolgs.

An extended form of the root, *bhleu- "to swell, well up, overflow," forms all or part of: affluent; bloat; confluence; effluent; effluvium; efflux; fluctuate; fluent; fluid; flume; fluor; fluorescence; fluoride; fluoro-; flush (v.1) "spurt, rush out suddenly, flow with force;" fluvial; flux; influence; influenza; influx; mellifluous; phloem; reflux; superfluous.
Related entries & more 
fluctuate (v.)
1630s, from Latin fluctuatus, past participle of fluctuare "to undulate, to move in waves," from fluctus "a wave, billow, surge, a flowing," from past participle of fluere "to flow" (see fluent). Related: Fluctuated; fluctuates; fluctuating.
Related entries & more 
Advertisement
wave (n.)
"moving billow of water," 1520s, alteration (by influence of wave (v.)) of Middle English waw, which is from Old English wagian "to move to and fro," from Proto-Germanic *wag- (source also of Old Saxon, Old High German wag, Old Frisian weg, Old Norse vagr "water in motion, wave, billow," Gothic wegs "tempest"), probably from PIE root *wegh- "to go, move." The usual Old English word for "moving billow of water" was .

The "hand motion" meaning is recorded from 1680s; meaning "undulating line" is recorded from 1660s. Of people in masses, first recorded 1852; in physics, from 1832. Sense in heat wave is from 1843. The crowd stunt in stadiums is attested under this name from 1984, the thing itself said to have been done first Oct. 15, 1981, at the Yankees-A's AL championship series game in the Oakland Coliseum; soon picked up and popularized at University of Washington. To make waves "cause trouble" is attested from 1962.
Related entries & more 
fluctuation (n.)

mid-15c., from Old French fluctuacion (12c.) or directly from Latin fluctuationem (nominative fluctuatio) "a wavering, vacillation," noun of action from past-participle stem of fluctuare "to undulate, to move in waves," from fluctus "a wave, billow, surge, a flowing," from past participle of fluere "to flow" (see fluent).

Related entries & more 
undine (n.)
female water spirit, 1821, from Modern Latin Undina (1650s), coined by Paracelsus ("De Nymphis") in his alchemical system, from Latin unda "a wave, billow" (from PIE root *wed- (1) "water; wet"). Popularized by German romance "Undine, eine Erzählung" (1811) by Baron F.H.C. La Motte Fouqué. Undinism (1928) was coined by sex researcher Havelock Ellis to describe the fetish for urine (which Ellis had); nowadays it would be called urophilia.
Related entries & more 
vogue (n.)

1570s, the vogue, "height of popularity or accepted fashion," from French vogue "fashion, success;" also "drift, swaying motion (of a boat)" literally "a rowing," from Old French voguer "to row, sway, set sail" (15c.), probably from a Germanic source. Compare Old High German wagon "to float, fluctuate," literally "to balance oneself;" German Woge "wave, billow," wogen "fluctuate, float" (from PIE root *wegh- "to go, move").

Perhaps the notion is of being "borne along on the waves of fashion." Italian voga "a rowing," Spanish boga "rowing," but colloquially "fashion, reputation" also probably are from the same Germanic source. Phrase in vogue "having a prominent place in popular fashion" first recorded 1643. The fashion magazine began publication in 1892.

Related entries & more 
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.

Related entries & more