Etymology
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multiplicand (n.)

"number multiplied or to be multiplied by another number," 1590s, from Latin multiplicandus "to be multiplied," gerundive of multiplicare "to multiply, increase" (see multiply).

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No. 
as an abbreviation meaning (and pronounced) "number," 1660s, from Latin numero, ablative singular of numerus (see number (n.)).
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numerology (n.)

"study of the occult meaning of numbers, divination by numbers," 1911, a hybrid from Latin numerus "a number" (see number (n.)) + Greek -logia (see -logy). A correct formation would be arithmology, from Greek arithmos "number." Related: Numerological; numerologist.

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drainage (n.)

1650s, "act or process of draining," from drain (v.) + -age. Sense of "the water carried off by a system of rivers" is by 1860. Meaning "system by means of which something is drained" is by 1878.

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divisor (n.)

"a number by which another number is divided," mid-15c., divisour, from Latin divisor, agent noun from dividere "to divide" (see divide (v.)).

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A-1 

also A1, A-one, "first-rate," 1837 (in Dickens); a figurative use from Lloyd's of London marine insurance company's system for selective rating of merchant vessels ("Register of British and Foreign Shipping"), where it is the designation for ships in first-class condition. The letter refers to the condition of the hull of the ship itself, and the number rating to the equipment. Also used in equivalent ratings in U.S., where colloquially it is sometimes expanded to A No. 1 (which is attested by 1848 as top rating of entries in an agricultural fair).

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tetrad (n.)
"the number four, collection of four things," 1650s, from Greek tetras (combining form tetrad-) "group of four, number four" (from PIE root *kwetwer- "four").
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VHS 
1982, initialism (acronym) of Video Home System.
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metric (adj.)

"pertaining to the system of weights and measures based on the meter," 1855, from French métrique, from mèter (see meter (n.2)). In this sense, metrical is attested from 1797. Metric system is attested by 1855.

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spherical (adj.)
1520s, from sphere + -ical. Related: Spherically. A spherical number (1640s) is one whose powers always terminate in the same digit as the number itself (5, 6, and 10 are the only ones).
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