Etymology
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unit (n.)
1560s, "single number regarded as an undivided whole," alteration of unity on the basis of digit. Popularized in John Dee's English translation of Euclid, to express Greek monas (Dee says unity formerly was used in this sense). Meaning "single thing regarded as a member of a group" is attested from 1640s. Extended sense of "a quantity adopted as a standard of measure" is from 1738. Sense of "group of wards in a hospital" is attested from 1893.
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weight (n.)

Old English gewiht "weighing, weight, downward force of a body, heaviness," from Proto-Germanic *wihti- (source also of Old Norse vætt, Danish vegt, Old Frisian wicht, Middle Dutch gewicht, German Gewicht), from *weg- (see weigh).

Figurative sense of "burden" is late 14c. To lose weight "get thinner" is recorded from 1961. Weight Watcher as a trademark name dates from 1960. To pull one's weight (1921) is from rowing. To throw (one's) weight around figuratively is by 1922. Weight-training is from 1945. Weight-lifting is from 1885; weight-lifter (human) from 1893.

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weight (v.)
"to load with weight," 1747 (figuratively, of the mind, from 1640s), from weight (n.). Of horses in a handicap race, 1846. Sense in statistics is recorded from 1901. Related: Weighted; weighting.
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feather-weight (n.)
also featherweight, "lightest weight allowable by rules," 1812 (earlier as simply feather, 1760), from feather (n.) + weight (n.). Originally in horse-racing; boxing use as a specific weight class dates from 1889.
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dead-weight (n.)

also deadweight, 1650s, "weight of an inert body," from dead (adj.) + weight (n.). Hence, "a heavy or oppressive burden" (1721).

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paper-weight (n.)

"small, heavy object used to hold down loose papers," by 1832, from paper (n.) + weight (n.).

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pennyweight (n.)

unit of measure equal to the weight of one penny, Old English penega gewiht, originally the weight of a silver penny (22 grains); see penny + weight (n.).

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lira (n.)
Italian monetary unit, 1610s, from Italian lira, literally "pound," from Latin libra "pound (unit of weight);" see Libra, and compare livre. There also was a Turkish lira.
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mark (n.2)

"unit of money or weight," late Old English marc, a unit of weight (chiefly for gold or silver) equal to about eight ounces, probably from Old Norse mörk "unit of weight," cognate with German Mark and probably ultimately a derivative of mark (n.1), perhaps in a sense of "imprinted weight or coin." It was a unit of account in England into 18c., perhaps originally introduced by the Danes, but never the name of a particular coin.

The word is found in all the Germanic and Romanic languages (compare Old Frisian merk, Dutch mark, Medieval Latin marca, French marc (11c.), Spanish and Italian marco); in English it was used from 18c. in reference to various continental coinages, especially the silver money of Germany first issued 1875.

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caddy (n.)
"small box for tea," 1792, from catty (1590s), Anglo-Indian unit of weight, from Malay (Austronesian) kati, a unit of weight. The catty was adopted as a standard mid-18c. by the British in the Orient and fixed in 1770 by the East India Company at a pound and a third. Apparently the word for a measure of tea was transferred to the chest it was carried in.
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