Etymology
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negative (adj.)

c. 1400, negatif, "expressing denial" (a sense now rare or obsolete), from Anglo-French negatif (early 14c.), Old French negatif (13c.) and directly from Latin negativus "that which denies," from negat-, past-participle stem of negare "deny, say no" (see deny).

The meaning "expressing negation" is from c. 1500; that of "characterized by absence of that which is affirmative or positive" is from 1560s. Algebraic sense, denoting quantities which are a subtraction from zero, is from 1670s. The electricity sense is from 1755.

Negative Capability, that is when a man is capable of being in uncertainties, Mysteries, doubts without any irritable reaching after fact and reason. [John Keats, letter, Dec. 21, 1817]

Related: Negatively.

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rh- 

consonantal digraph, an initial sequence used in Latin (and thus in English words from Latin) to represent Greek initial aspirated r-. The medial Greek form of it usually is represented by -rrh-, as in catarrh, diarrhea, hemorrhage, myrrh, Pyrrhic. As it was pronounced as simply "r" in Middle English (as in Old French and Spanish), the -h- tended to be dropped in spelling but was restored in early Modern English with the classical revival.

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Rh. 

chemical symbol of rhodium (q.v.). 

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blood (n.)

Old English blod "blood, fluid which circulates in the arteries and veins," from Proto-Germanic *blodam "blood" (source also of Old Frisian blod, Old Saxon blôd, Old Norse bloð, Middle Dutch bloet, Dutch bloed, Old High German bluot, German Blut, Gothic bloþ), according to some sources from PIE *bhlo-to-, perhaps meaning "to swell, gush, spurt," or "that which bursts out" (compare Gothic bloþ "blood," bloma "flower"), from suffixed form of root *bhel- (3) "to thrive, bloom." But Boutkan finds no certain IE etymology and assumes a non-IE origin.

There seems to have been an avoidance in Germanic, perhaps from taboo, of other PIE words for "blood," such as *esen- (source of poetic Greek ear, Old Latin aser, Sanskrit asrk, Hittite eshar); also *krew-, which seems to have had a sense of "blood outside the body, gore from a wound" (source of Latin cruour "blood from a wound," Greek kreas "meat"), but which came to mean simply "blood" in the Balto-Slavic group and some other languages.

Inheritance and relationship senses (also found in Latin sanguis, Greek haima) emerged in English by mid-13c. The meanings "person of one's family, race, kindred; offspring, one who inherits the blood of another" are late 14c. As the fluid of life (and the presumed seat of the passions), blood has stood for "temper of mind, natural disposition" since c. 1300 and been given many figurative extensions. The slang meaning "hot spark, a man of fire" [Johnson] is from 1560s. Blood pressure is attested from 1862. Blood money is from 1530s; originally money paid for causing the death of another.

Blood type is from 1928. That there were different types of human blood was discovered c. 1900 during early experiments in transfusion. To get blood from a stone "do the impossible" is from 1660s. Expression blood is thicker than water is attested by 1803, in reference to family ties of those separated by distance. New (or fresh) blood, in reference to new members of an organization or group, especially ones bringing new ideas and fresh vigor or strength, is from 1880.

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blood (v.)

1590s, "to smear or stain with blood;" 1620s, "to cause to bleed," from blood (n.). Meaning "to give (a hunting animal) its first taste of blood" is from 1781. Related: Blooded; blooding.

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negative (n.)

late 14c., "a prohibition" (a sense now obsolete), also "absence, nonexistence; opposite," from Old French negatif and directly from Latin negativus (see negative (adj.)).

Meaning "a negative statement" is from 1560s. Sense of "that side of a question which denies what the opposite side affirms" is from 1570s. Meaning "the right or power of refusing assent" is from 1610s. Meaning "a negative quality" is from 1640s. In mathematics, "a negative number," from 1706. Photographic sense of "image in which the lights and shades are the opposite of those in nature" is recorded by 1853. As a response, "I refuse, disagree, no," from 1945, originally in radio communication. 

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negative (v.)

"reject, refuse to accept," 1706, from negative (adj.).

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blue-blood (adj.)

1809 in reference to the blood that flows in the veins of the old and aristocratic families of Spain, translating Spanish sangre azul, claimed by certain families of Castile that held themselves uncontaminated by Moorish or Jewish admixture; the term probably is from the notion of the visible veins of people of fair complexion. In reference to English families by 1827. As a noun, "member of an old and aristocratic family," by 1877. See blue (adj.1) + blood (n.).

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Rh factor 

1942, from the first letters of rhesus; so called because the blood group, and its effects, were discovered in the blood of rhesus monkeys (1941).

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half-blood (n.)

"person of mixed race," 1826; see half + blood (n.). As an adjective, "born of one parent the same and one different," from 1550s. Half-blooded as an adjective in this sense is from c. 1600.

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