Etymology
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play (v.)

Middle English pleien, from Old English plegan, plegian "move lightly and quickly, occupy or busy oneself, amuse oneself; engage in active exercise; frolic; engage in children's play; make sport of, mock; perform music," from Proto-West Germanic *plegōjanan "occupy oneself about" (source also of Old Saxon plegan "vouch for, take charge of," Old Frisian plega "tend to," Middle Dutch pleyen "to rejoice, be glad," German pflegen "take care of, cultivate"), which is apparently connected to the root of plight (v.), but the ultimate etymology is uncertain and the phonetic development is difficult to explain.

Meaning "to take part in" a martial or athletic game is from c. 1200. It has been opposed to work (v.) since late 14c. Meaning "perform or act on the stage" (transitive) is by late 14c., as are the senses of "take the role of" and "make a pretense of, make believe" and "act thoughtlessly or wantonly." Sense of "put forward, move, throw, lay on the table, etc." in the course of a game or contest is by 1560s of chess pieces, 1670s of playing cards. Sense of "operate or cause to operate with continuous or repeated action" is from 1590s. Meaning "to cause (a recording) to reproduce what is on it" is by 1903, probably from the "make music" sense. Related: Played; playing.

Many expressions are from the stage, sports and games, or music, and it is not always easy to say which is from which. To play up "emphasize" is from 1909 (perhaps originally "play music more vigorously"); to play down "minimize" is from 1930; to play along "pretend to agree or cooperate" is from 1929. To play fair "be nice" is from mid-15c. To play house as a children's activity is from 1958.

To play for keeps is from 1861, originally of marbles or other children's games with tokens. To play (something) safe is from 1911; to play favorites is attested from 1902.  To play second fiddle in the figurative sense is from 1809 ("Gil Blas"). To play into the hands (of someone) "act in such a way as to give the advantage to one's opponent or a third party" is from 1705. For play the _______ card see card (n.1). For play the field see field (n.). To play with oneself "masturbate" is from 1896 (to play with "have sexual intercourse with" is from mid-13c.). Playing-card "one of a pack of cards used for playing games" is from 1540s.

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life (n.)

Old English life (dative lif) "animated corporeal existence; lifetime, period between birth and death; the history of an individual from birth to death, written account of a person's life; way of life (good or bad); condition of being a living thing, opposite of death; spiritual existence imparted by God, through Christ, to the believer," from Proto-Germanic *leiban (source also of Old Norse lif "life, body," Old Frisian, Old Saxon lif "life, person, body," Dutch lijf "body," Old High German lib "life," German Leib "body"), properly "continuance, perseverance," from PIE root *leip- "to stick, adhere."

The noun associated with live (v.) "to live," which is literally "to continue, remain." Extended 1703 to inanimate objects, "term of duration or existence." Sense of "vitality, energy in action, expression, etc." is from 1580s. Meaning "conspicuously active part of human existence, pleasures or pursuits of the world or society" is by 1770s. Meaning "cause or source of living" led to the sense "vivifying or animating principle," and thus "one who keeps things lively" in life of the party (1787). Meaning "imprisonment for life, a life sentence" is from 1903. Paired alliteratively with limb from 1640s. Not on your life "by no means" is attested from 1896.

In gaming, an additional turn at play for a character; this transferred use was prefigured by uses in card-playing (1806), billiards (1856), etc., in reference to a certain number of chances or required objects without which one's turn at the game fails. The life "the living form or model, semblance" is from 1590s. Life-and-death "of dire importance" is from 1822; life-or-death (adj.) is from 1897. Life-jacket is from 1840; life-preserver from 1630s of anything that is meant to save a life, 1803 of devices worn to prevent drowning. Life-saver is from 1883, figurative use from 1909, as a brand of hard sugar candy from 1912, so called for shape.

Life-form is from 1861; life-cycle is from 1855; life-expectancy from 1847; life-history in biology from 1870; life-science from 1935. Life-work "the labor to which one's life has been devoted" is from 1848. Expression this is the life is from 1919; verbal shrug that's life is from 1924 (earlier such is life, 1778).

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run (v.)

Old English, "move swiftly by using the legs, go on legs more rapidly than walking," also "make haste, hurry; be active, pursue or follow a course," and, of inanimate things, "to move over a course."

The modern verb is a merger of two related Old English words, in both of which the initial two letters sometimes switched places. The first is intransitive rinnan, irnan "to run, flow, run together" (past tense ran, past participle runnen), which is cognate with Middle Dutch runnen, Old Saxon, Old High German, Gothic rinnan, German rinnen "to flow, run."

The second is Old English transitive weak verb ærnan, earnan "ride, run to, reach, gain by running" (probably a metathesis of *rennan), from Proto-Germanic *rannjanan, causative of the root *ren- "to run." This is cognate with Old Saxon renian, Old High German rennen, German rennen, Gothic rannjan.

Watkins says both are from PIE *ri-ne-a-, nasalized form of root *rei- "to run, flow," but Boutkan's sources find this derivation doubtful based on the poor attestation of supposed related forms, and he lists it as of "No certain IE etymology."

Of streams, etc., "to flow," from late Old English. From c. 1200 as "take flight, retreat hurriedly or secretly." Phrase run for it "take flight" is attested from 1640s.

Also from c. 1200 as "compete in a race." Extended to "strive for any ends," especially "enter a contest for office or honors, stand as a candidate in an election" (1826, American English).

Of any sort of hurried travel, c. 1300. From early 13c. as "have a certain direction or course." By c. 1300 as "keep going, extend through a period of time, remain in existence." Specifically of theater plays by 1808. Of conveyances, stage lines, etc., "perform a regular passage from place to place" by 1817.

Of machinery or mechanical devices, "go through normal or allotted movements or operation," 1560s. Of colors, "to spread in a fabric when exposed to moisture," 1771. Of movie film, "pass between spools," hence "be shown," by 1931.

The meaning "carry on" (a business, etc.) is by 1861, American English; hence extended senses of "look after, manage." As "publish or print in a newspaper or magazine," by 1884. 

Many senses are via the notion of "pass into or out of a certain state." To run dry "cease to yield water or milk" (1630s). In commerce, "be of a specified price, size, etc.," by 1762. To run low "be nearly exhausted" is by 1712; to run short "exhaust one's supply" is from 1752; to run out of in the same sense is from 1713. To run on "keep on, continue without pause or change" is from 1590s.

The transitive sense of "cause to run" was in Old English. By late 15c. as "to pierce, stab," hence 1520s as "thrust through or into something." The meaning "enter (a horse) in a race" is from 1750. The sense of "cause a mechanical device to keep moving or working" is by 1817.

Many figurative uses are from horseracing or hunting (such as to run (something) into the ground "carry to excess, exhaust by constant pursuit," 1836, American English).

To run across "meet by chance, fall in with" is attested from 1855, American English. To run into in this sense is by 1902. To run around with "consort with" is from 1887.

In reference to fevers by 1918. To run a (red) traffic signal is by 1933. Of tests, experiments, etc., by 1947. Of computers by 1952. Time has been running out since c. 1300. To run in the family is by 1771. The figurative expression run interference (1929) is from U.S. football. To run late is from 1954.

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