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rotor (n.)

Related entries & more 1873, an irregular shortening of rotator, originally in mathematics. Mechanical sense of "rotating part of a motor" is attested by 1903; specifically of helicopters from 1930.

factor (v.)1610s, "act as an agent, manage," from factor (n.). The use in mathematics is attested from 1837. Related: Factored; factoring.

Related entries & more radicand (n.)

Related entries & more in mathematics, the number under a radical sign, by 1843, from German, from Modern Latin radicandus, gerundive of radicare "to take root," from radix "root" (from PIE root *wrād- "branch, root").

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-ics in the names of sciences or disciplines (acoustics, aerobics, economics, etc.), a 16c. revival of the classical custom of using the neuter plural of adjectives with Greek -ikos "pertaining to" (see -ic) to mean "matters relevant to" and also as the titles of treatises about them. Subject matters that acquired their English names before c. 1500, however, tend to be singular in form (arithmetic, logic, magic, music, rhetoric). The grammatical number of words in -ics (mathematics is/mathematics are) is a confused question.

Related entries & more frustum (n.)"remaining piece after a part has been cut off," 1650s, in mathematics, from Latin frustum "piece broken off," from PIE *bhrus-to-, from root *bhreu- "to cut, break up" (see bruise (v.)).

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