Etymology
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gram (n.)

also gramme, metric unit of weight, 1797, from French gramme (18c.), from Late Latin gramma "small weight," from Greek gramma "small weight," a special use of the classical word meaning "a letter of the alphabet" (see -gram). Adopted into English about two years before it was established in France as a unit in the metric system by law of 19 frimaire, year VIII (1799). "There seems to be no possible objection to adopting the more convenient shorter form, except that the -me records the unimportant fact that the word came to us through French" [Fowler].

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stain (v.)

late 14c., "damage or blemish the appearance of," probably representing a merger of Old Norse steina "to paint, color, stain," and a shortened form of Middle English disteynen "to discolor or stain," from Old French desteign-, stem of desteindre "to remove the color" (Modern French déteindre), from des- (from Latin dis- "remove;" see dis-) + Old French teindre "to dye," from Latin tingere (see tincture). Meaning "to color" (fabric, wood, etc.) is from 1650s. Intransitive sense "to become stained, take stain" is from 1877. Related: Stained; staining. Stained glass is attested from 1791.

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-gram 

noun word-forming element, "that which is written or marked," from Greek gramma "that which is drawn; a picture, a drawing; that which is written, a character, an alphabet letter, written letter, piece of writing;" in plural, "letters," also "papers, documents of any kind," also "learning," from stem of graphein "to draw or write" (see -graphy). Some words with it are from Greek compounds, others are modern formations. Alternative -gramme is a French form.

From telegram (1850s) the element was abstracted by 1959 in candygram, a proprietary name in U.S., and thereafter put to wide use as a second element in forming new commercial words, such as Gorillagram (1979), stripagram (1981), and, ultimately, Instagram (2010). The construction violates Greek grammar, as an adverb could not properly form part of a compound noun. An earlier instance was the World War II armed services slang latrinogram "latrine rumor, barracks gossip" (1944).

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stain (n.)

1560s, "act of staining," from stain (v.). Meaning "a stain mark, discoloration produced by foreign matter" is from 1580s. Meaning "dye used in staining" is from 1758.

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nanogram (n.)

"one-billionth of a gram," 1951, from nano- + gram.

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milligram (n.)

also milligramme, "one-thousandth part of a gram," 1802, from French milligramme; see milli- + gram.

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taint (n.)

c. 1600, "stain, spot," from Old French teint "color, hue, dye, stain," from Latin tinctus "a dyeing," from tingere "to dye" (see tincture). Meaning "a moral stain, corruption, contaminating influence" is from 1610s.

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centigram (n.)

also centigramme, metric measure of weight, "one hundredth of a gram," 1801, from French centigramme; see centi- + gram.

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electroencephalogram (n.)

1934, from electro- + encephalo-, combining form of Modern Latin encephalon "brain" (see encephalitis) + -gram.

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