Etymology
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go on (v.)
1580s, "advance, proceed," from go (v.) + on (adv.). Meaning "behave, carry on" is from 1777; especially "to talk volubly" (1863). As an expression of derision by 1886.
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go-go (adj.)
1964, "fashionable," from slang adjective go "fashionable" (1962); see go (n.). First appearance of go-go dancer is from 1965.
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on- 

the preposition and adverb on used as a prefix; Old English on-, an-.

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-on 
subatomic particle suffix, from ion.
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on (prep., adv.)

"in a position above and in contact with; in such a position as to be supported by;" also noting the goal to which some action is or has been directed; "about, concerning, regarding; in a position to cover;" as an adverb, "in or into a position in contact with and supported by the top or upper part of something; in or into place; in place for use or action; into movement or action; in operation," Old English on, unstressed variant of an "in, on, into," from Proto-Germanic *ana "on" (source also of Dutch aan, German an, Gothic ana "on, upon"), from PIE root *an- (1) "on" (source also of Avestan ana "on," Greek ana "on, upon," Latin an-, Old Church Slavonic na, Lithuanian nuo "down from").

Also used in Old English in many places where we now would use in. From 16c.-18c. (and still in northern England dialect) often reduced to o'. Phrase on to "aware" is from 1877.

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back (n.)

Old English bæc "back," from Proto-Germanic *bakam (cognates: Old Saxon and Middle Dutch bak, Old Frisian bek), with no known connections outside Germanic. In other modern Germanic languages the cognates mostly have been ousted in this sense by words akin to Modern English ridge (such as Danish ryg, German Rücken).

Many Indo-European languages show signs of once having distinguished the horizontal back of an animal (or a mountain range) from the upright back of a human. In other cases, a modern word for "back" may come from a word related to "spine" (Italian schiena, Russian spina) or "shoulder, shoulder blade" (Spanish espalda, Polish plecy).

By synecdoche, "the whole body," especially with reference to clothing. Meaning "upright part of a chair" is from 1520s. To turn (one's) back on (someone or something) "ignore" is from early 14c. As a U.S. football position by 1876, so called from being behind the line of rushers; further distinguished according to relative position as quarterback, halfback, fullback.

To know (something) like the back of one's hand, implying familiarity, is first attested 1893 in a dismissive speech made to a character in Robert Louis Stevenson's "Catriona":

If I durst speak to herself, you may be certain I would never dream of trusting it to you; because I know you like the back of my hand, and all your blustering talk is that much wind to me.

The story, a sequel to "Kidnapped," has a Scottish setting and context, and the back of my hand to you was noted in the late 19th century as a Scottish expression meaning "I will have nothing to do with you" [see Longmuir's edition of Jamieson's Scottish dictionary]. In English generally, the back of (one's) hand has been used to imply contempt and rejection at least since 1300. Perhaps the connection of a menacing dismissal is what made Stevenson choose that particular anatomical reference.

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go (n.)

1727, "action of going," from use of go (v.) to start a race, etc. Meaning "an incident, an occurrence, affair, piece of business" is from 1796. Meaning "power of going, dash, vigor" is from 1825, colloquial, originally of horses. The sense of "an attempt, a try or turn at doing something" (as in give it a go, have a go at) is from 1825 (earlier it meant "a delivery of the ball in skittles," 1773). Meaning "something that goes, a success" is from 1876. Phrase on the go "in constant motion" is from 1843. Phrase from the word go "from the beginning" is by 1834. The go "what is in fashion" is from 1793. No go "of no use" is from 1825.

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go (adj.)
"in order," 1951, originally in aerospace jargon, from go (v.).
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go (v.)

Old English gan "to advance, walk; depart, go away; happen, take place; conquer; observe, practice, exercise," from West Germanic *gaian (source also of Old Saxon, Old Frisian gan, Middle Dutch gaen, Dutch gaan, Old High German gan, German gehen), from PIE root *ghē- "to release, let go; be released" (source also of Sanskrit jihite "goes away," Greek kikhano "I reach, meet with"), but there does not seem to be general agreement on a list of cognates.

A defective verb throughout its recorded history; the Old English past tense was eode, a word of uncertain origin but evidently once a different verb (perhaps connected to Gothic iddja); it was replaced 1400s by went, past tense of wenden "to direct one's way" (see wend). In northern England and Scotland, however, eode tended to be replaced by gaed, a construction based on go. In modern English, only be and go take their past tenses from entirely different verbs.

The word in its various forms and combinations takes up 45 columns of close print in the OED. Meaning "cease to exist" is from c. 1200; that of "to appear" (with reference to dress, appearance, etc.) is from late 14c.; that of "to be sold" is from early 15c. Meaning "to be known" (with by) is from 1590s; that of "pass into another condition or state" is from 1580s. From c. 1600 as "to wager," hence also "to stand treat," and to go (someone) better in wagering (1864). Meaning "say" emerged 1960s in teen slang. Colloquial meaning "urinate or defecate" attested by 1926, euphemistic (compare Old English gong "a privy," literally "a going").

To go back on "prove faithless to" is from 1859; to go under in the figurative sense "to fail" is from 1849. To go places "be successful" is by 1934.

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back (v.)
mid-15c., "to keep something back, hinder," from back (adv.). Meaning "cause to move back" is from 1781. Intransitive sense "move or go back" is from late 15c. Meaning "furnish with a back or backing" is from 1728, from back (n.). Meaning "to support" (as by a bet) is attested from 1540s. Related: Backed; backing.
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