Etymology
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spring (n.3)
"act of springing or leaping," late 14c., from spring (v.). The elastic wire coil that returns to its shape when stretched is so called from early 15c., originally in clocks and watches. As a device in carriages, coaches, etc., it is attested from 1660s.
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natural (n.)

"person with a natural gift or talent," 1925, originally in prizefighting, from natural (adj.). But an older sense is almost opposite to this, "half-wit, idiot" (one "naturally deficient" in intellect), which was in use 16c. to 19c. In Middle English, the word as a noun meant "natural capacity, physical ability or power" (early 14c.), and it was common in sense "a native of a place" in Shakespeare's day. Also in 17c., "a mistress."

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natural (adj.)

c. 1300, naturel, "of one's inborn character; hereditary, innate, by birth or as if by birth;" early 14c. "of the world of nature (especially as opposed to man)," from Old French naturel "of nature, conforming to nature; by birth," and directly from Latin naturalis "by birth, according to nature," from natura "nature" (see nature).

Of events, features, etc., "existing in nature as a result of natural forces" (that is, not caused by accident, human agency, or divine intervention), late 14c. From late 14c. of properties, traits, qualities, "proper, suitable, appropriate to character or constitution;"  from late 15c. as "native, native-born." Also late 15c. as "not miraculous, in conformity with nature," hence "easy, free from affectation" (c. 1600). Of objects or substances, "not artificially cultivated or created, existing in nature" c. 1400. As a euphemism for "illegitimate, bastard" (of children), it is recorded from c. 1400, on the notion of blood kinship (but not legal status).

Natural science, that pertaining to physical nature, is from late 14c.;  natural history meaning more or less the same thing is from 1560s (see history).  Natural law "the expression of right reason or the dictate of religion inhering in nature and man and having ethically binding force as a rule of civil conduct" is from late 14c. Natural order "apparent order in nature" is from 1690s. Natural childbirth is attested by 1898. Natural life, usually in reference to the duration of life, is from mid-15c.; natural death, one without violence or accident, is from mid-15c. To die of natural causes is from 1570s.

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spring (n.1)

"season following winter, first of the four seasons of the year; the season in which plants begin to rise," by 1540s, short for spring of the year (1520s), a special sense of an otherwise now-archaic spring (n.) "act or time of springing or appearing; the first appearance; the beginning, birth, rise, or origin" of anything (see spring v., and compare spring (n.2), spring (n.3)). The earliest form seems to have been springing time (late 14c.).

The notion is of the "spring of the year," when plants begin to rise and trees to bud (as in spring of the leaf, 1520s). The Middle English noun also was used of sunrise, the waxing of the moon, rising tides, sprouting of the beard or pubic hair, etc.; compare 14c. spring of dai "sunrise," spring of mone "moonrise." Late Old English spring meant "carbuncle, pustule."

It replaced Old English lencten (see Lent) as the word for the vernal season.  Other Germanic languages tend to take words for "fore" or "early" as their roots for the season name (Danish voraar, Dutch voorjaar, literally "fore-year;" German Frühling, from Middle High German vrueje "early"). In 15c. English, the season also was prime-temps, after Old French prin tans, tamps prim (French printemps, which replaced primevère 16c. as the common word for spring), from Latin tempus primum, literally "first time, first season."

Spring fever is from 1843 as "surge of romantic feelings;" earlier of a type of disease or head-cold prevalent in certain places in spring; Old English had lenctenadle. First record of spring cleaning in the domestic sense is by 1843 (in ancient Persia, the first month, corresponding to March-April, was Adukanaiša, which apparently means "Irrigation-Canal-Cleaning Month;" Kent, p.167). Spring chicken "small roasting chicken" (usually 11 to 14 weeks) is recorded from 1780; transferred sense of "young person" first recorded 1906. Baseball spring training attested by 1889, earlier of militias, etc.

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spring (v.)

Old English springan "to leap, burst forth, fly up; spread, grow," (class III strong verb; past tense sprang, past participle sprungen), from Proto-Germanic *sprengan (source also of Old Norse, Old Frisian springa, Middle Dutch springhen, Dutch Related: springen, Old Saxon and Old High German springan, German springen), from PIE *sprengh-, nasalized form of root *spergh- "to move, hasten, spring" (source also of Sanskrit sprhayati "desires eagerly," Greek sperkhesthai "to hurry").

In Middle English, it took on the role of causal sprenge, from Old English sprengan (as still in to spring a trap, etc.). Meaning "to cause to work or open," by or as by a spring mechanism, is from 1828. Meaning "to announce suddenly" (usually with on) is from 1876. Meaning "to release" (from imprisonment) is from 1900. Slang meaning "to pay" (for a treat, etc.) is recorded from 1906.

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spring (n.2)
"source of a stream or river, flow of water rising to the surface of the earth from below," Old English spring "spring, source, sprinkling," from spring (v.) on the notion of the water "bursting forth" from the ground. Rarely used alone in Old English, appearing more often in compounds, such as wyllspring "wellspring," espryng "water spring." Figurative sense of "source or origin of something" is attested from early 13c. Cognate with Old High German sprung "source of water," Middle High German sprinc "leap, jump; source of water."
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spring-house (n.)
also springhouse, 1762, from spring (n.2) + house (n.).
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natural-born (adj.)

"so by nature, born so," 1580s, from natural (adj.) + born.

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vernal (adj.)
"pertaining to spring," 1530s, from Late Latin vernalis "of the spring," from vernus "of spring," from Latin ver "the spring, spring-time," from PIE *wesr- "the spring" (source also of Old Norse var "spring," Greek ear, Armenian gar-un, Sanskrit vasantah, Persian bahar, Old Church Slavonic vesna "spring," Lithuanian vasara "summer").
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fountain (n.)

early 15c., "spring of water that collects in a pool," from Old French fontaine "natural spring" (12c.), from Medieval Latin fontana "fountain, a spring" (source of Spanish and Italian fontana), from post-classical noun use of fem. of Latin fontanus "of a spring," from fons (genitive fontis) "spring (of water)," from PIE root *dhen- (1) "to run, flow" (source also of Sanskrit dhanayati, Old Persian danuvatiy "flows, runs").

The extended sense of "artificial jet of water" (and the structures that make them) is first recorded c. 1500. Hence also fountain-pen (by 1823), so called for the reservoir that supplies a continuous flow of ink. "A French fountain-pen is described in 1658 and Miss Burney used one in 1789" [Weekley]. Fountain of youth, and the story of Ponce de Leon's quest for it, seem to have been introduced in American English by Hawthorne's "Dr. Heidegger's Experiment" (January 1837).

"Did you never hear of the 'Fountain of Youth'?" asked Dr. Heidegger, "which Ponce de Leon, the Spanish adventurer, went in search of two or three centuries ago?"
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