Etymology
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hairpin (n.)
also hair-pin, 1788 (two words), from hair + pin (n.). A hairpin turn, etc., is from 1906. Hairpin (or clothespin) was American English slang for "person" c. 1880-1910, especially in the expression "That's the kind of hairpin I am."
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hair-raising (adj.)
"exciting," 1837, from hair + raise (v.). In 19c. works, sometimes as jocular mock-classical tricopherous.
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hair-shirt (n.)
garment of ascetics and penitents, 1680s, from hair + shirt. Figurative use by 1884. Earlier, such a garment was called simply a hair (c. 1200); and compare haircloth.
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hair-splitting (n.)
"making over-nice distinctions," by 1739, from hair + verbal noun from split (v.). To split hairs "make over-fine distinctions" is first recorded 1650s, as to cut the hair. Hair also being 18c. slang for "female pudendum," hair-splitter was noted in 1811 as slang for "penis."
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hairstyle (n.)
also hair-style, "way of wearing the hair," 1913, from hair + style (n.).
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hair-trigger (n.)

1795; Figurative use by 1841. Hair perhaps in reference to the slight pressure required to activate it.

The difference between a hair-trigger and a common trigger is this—the hair-trigger, when set, lets off the cock by the slightest touch, whereas the common trigger requires a considerable degree of force, and consequently is longer in its operation. [Charles James, "Military Dictionary," London, 1802]
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hairy (adj.)
early 14c., "covered with hair, rough, shaggy," from hair + -y (2). From 1848 in slang sense of "difficult," perhaps from the notion of "rugged, rough." Farmer calls this "Oxford slang." Related: Hairiness. For adjectives Old English had hæriht, hære "hairy;" hæren "of hair."
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Haiti 
from Arawak haiti "land of mountains," and probably originally the name of the whole island. Related: Haitian.
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hajj (n.)
also hadj, "the pilgrimage to Mecca," which every free Muslim is bound to make, as a religious duty, from Arabic hajj "pilgrimage," from hajja "he went on a pilgrimage." Related to Hebrew haghagh "he made a pilgrimage, celebrated a feast," hagh "a gathering." One who has made it is a hajji and afterward bears that title as a designation of honor.
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