Etymology
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primum mobile (n.)

"the first source of motion," mid-15c., from Medieval Latin (11c.), literally "the first movable thing;" see prime (adj.) + mobile.

In the Ptolemaic system of astronomy, the tenth or outermost of the revolving spheres of the universe, which was supposed to revolve from east to west in twenty-four hours, and to carry the others along with it in its motion; hence, any great or first source of motion. [Century Dictionary]

A translation of Arabic al-muharrik al-awwal "the first moving" (Avicenna). Englished by Chaucer as the firste Moeuyng (c. 1400). Old science also had primum frigidum "pure cold: an elementary substance, according to the doctrine of Parmenides."


 

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Brownian movement (n.)
"rapid oscillatory motion observed in very small particles," 1850, for Scottish scientist Dr. Robert Brown (1773-1858), who first described it.
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solvitur ambulando 
an appeal to practical experience for a solution or proof, Latin, literally "(the problem) is solved by walking," originally in reference to the proof by Diogenes the Cynic of the possibility of motion.
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jerk off (v.)

slang, "perform male masturbation," by 1896, from jerk (v.) denoting rapid pulling motion + off (adv.). Compare come off "experience orgasm" (17c.). Farmer and Henley ("Slang and Its Analogues") also lists as synonyms jerk (one's) jelly and jerk (one's) juice. The noun jerk off or jerkoff as an emphatic form of jerk (n.2) is attested by 1968. As an adjective from 1957.

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