Etymology
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rank (adj.)

Old English ranc "proud, overbearing, haughty, showy," senses now obsolete, from Proto-Germanic *rankaz (source also of Danish rank "right, upright," German rank "slender," Old Norse rakkr "straight, erect"), which is of uncertain origin, possibly related to Old Norse and Old English rinc "man, warrior." Related: Rankly; rankness.

In reference to plant growth, "vigorous, luxuriant, abundant, copious" (also figurative) it is recorded from c. 1300. The sense also evolved in Middle English to "large and coarse" (c. 1300), then to "corrupt, loathsome, foul" (mid-14c.), perhaps via the notion of "excessive and unpleasant," perhaps also influenced in this by French rance "rancid." Specifically as "having an offensive, strong smell" by 1520s. In Middle English also "brave, stout-hearted; splendid, admirable." In 17c. it also could mean "lewd, lustful."

The development of the word in Eng. is, however, far from clear, as the OE. uses are not quite the primitive ones. In ME. also it chiefly occurs in alliterative verse, app. more for convenience than to express definite meanings. In the later language the chief difficulty is to decide which of the more original senses are represented in the transferred uses. [OED]

Much used 16c. as a pejorative intensive (as in rank folly). This is possibly the source of the verb meanings "to reveal another's guilt" (1929, underworld slang) and that of "to harass, insult, abuse," 1934, African-American vernacular, though this also may be so called from the role of the activity in establishing social hierarchy (and thus from rank (n.)).

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melancholy (n.)

c. 1300, melancolie, malencolie, "mental disorder characterized by sullenness, gloom, irritability, and propensity to causeless and violent anger," from Old French melancolie "black bile; ill disposition, anger, annoyance" (13c.), from Late Latin melancholia, from Greek melankholia "sadness," literally (excess of) "black bile," from melas (genitive melanos) "black" (see melano-) + khole "bile" (see cholera).

Old medicine attributed mental depression to unnatural or excess "black bile," a secretion of the spleen and one of the body's four "humors," which help form and nourish the body unless altered or present in excessive amounts. The word also was used in Middle English for "sorrow, gloom" (brought on by love, disappointment, etc.), by mid-14c. As belief in the old physiology of humors faded out in the 18c. the word remained with a sense of "a gloomy state of mind," particularly when habitual or prolonged.

The Latin word also is the source of Spanish melancolia, Italian melancolia, German Melancholie, Danish melankoli, etc. Old French variant malencolie (also in Middle English) is by false association with mal "sickness."

When I go musing all alone,
Thinking of divers things fore-known,
When I build castles in the air,
Void of sorrow and void of fear,
Pleasing myself with phantasms sweet,
Methinks the time runs very fleet.
   All my joys to this are folly,
   Naught so sweet as melancholy.
When I lie waking all alone,
Recounting what I have ill done,
My thoughts on me then tyrannise,
Fear and sorrow me surprise,
Whether I tarry still or go,
Methinks the time moves very slow.
   All my griefs to this are jolly,
   Naught so sad as melancholy.
[Robert Burton, from "Anatomy of Melancholy," 17c.]
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fair (adj.)

Old English fæger "pleasing to the sight (of persons and body features, also of objects, places, etc.); beautiful, handsome, attractive," of weather, "bright, clear, pleasant; not rainy," also in late Old English "morally good," from Proto-Germanic *fagraz (source also of Old Saxon fagar, Old Norse fagr, Swedish fager, Old High German fagar "beautiful," Gothic fagrs "fit"), perhaps from PIE *pek- (1) "to make pretty" (source also of Lithuanian puošiu "I decorate").

The meaning in reference to weather preserves the oldest sense "suitable, agreeable" (opposed to foul (adj.)). Of the main modern senses of the word, that of "light of complexion or color of hair and eyes, not dusky or sallow" (of persons) is from c. 1200, faire, contrasted to browne and reflecting tastes in beauty. From early 13c. as "according with propriety; according with justice," hence "equitable, impartial, just, free from bias" (mid-14c.).

Of wind, "not excessive; favorable for a ship's passage," from late 14c. Of handwriting from 1690s. From c. 1300 as "promising good fortune, auspicious." Also from c. 1300 as "above average, considerable, sizable." From 1860 as "comparatively good."

The sporting senses (fair ball, fair catch, etc.) began to appear in 1856. Fair play is from 1590s but not originally in sports (earlier it meant "pleasant amusement," c. 1300, and foul play was "sinful amusement"). Fair-haired in the figurative sense of "darling, favorite" is from 1909. First record of fair-weather friends is from 1736 (in a letter from Pope published that year, written in 1730). The fair sex "women" is from 1660s, from the "beautiful" sense (fair as a noun meaning "a woman" is from early 15c.). Fair game "legitimate target" is from 1776, from hunting.

Others, who have not gone to such a height of audacious wickedness, have yet considered common prostitutes as fair game, which they might pursue without restraint. ["Advice from a Father to a Son, Just Entered into the Army and about to Go Abroad into Action," London, 1776]
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