Etymology
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constrictor (n.)

"that which constricts," 1735, originally "a muscle which draws parts together," agent noun in Latin form from constrict. Meaning "a large serpent which envelops and crushes its prey in its coils" is from 1790.

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popliteal (adj.)

"of or pertaining to the back of the knee," 1786, with -al (1) + Modern Latin popliteus (n.) "flat, triangular muscle at the back of the knee-joint," 1704, short for popliteus (musculus), from Latin poples "ham (of the leg)," which is of unknown origin.

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pectoral (adj.)

1570s, "of or pertaining to the breast or chest," from Latin pectoralis "of the breast," from pectus (genitive pectoris) "breast, chest," a word of unknown origin. De Vaan considers Old Irish ucht "breast, chest" as "a likely cognate, if it reflects earler *pektu-." Pectoral muscle is attested from 1610s.

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extensor (n.)
"muscle which serves to straighten or extend any part of the body," 1713, short for medical Latin musculus extensor, from Late Latin extensor "stretcher," agent noun from Latin extendere "spread out, spread" (see extend).
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rotator (n.)

1670s, "muscle which allows a part to be moved circularly," agent noun from Latin rotare "turn round, revolve" (see rotary). Also compare rotor. General mechanical sense of "one who or that which rotates" is by 1772. Related: Rotatory.

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washboard (n.)
also wash-board, clothes-cleaning device, 1882, from wash (v.) + board (n.1). As a percussion instrument, attested from 1925; in reference to abdominal muscles, recorded from 1950 in boxing jargon. Earlier such muscle development was described as checkerboard (1893).
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sphincter (n.)

1570s, from French sphincter, from Late Latin sphincter "contractile muscle," from Greek sphinkter "band, lace, anything that binds tight," from sphingein "to squeeze, bind," of unknown origin. First used in anatomical sense by Galen. There are several in the body; the one usually meant is the sphincter ani.

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indicator (n.)
1660s, "that which indicates or points out," from Late Latin indicator, agent noun from indicare "to point out, show" (see indication). As a finger muscle, from 1690s. As a steam-cylinder's pressure gauge, 1839. As a device on a motor vehicle to signal intention to change direction, 1932.
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levator (n.)
1610s in anatomy, "type of muscle that raises or elevates," from medical Latin levator (plural levatores) "a lifter," from Latin levatus, past participle of levare "to raise, lift up; make lighter" (from PIE root *legwh- "not heavy, having little weight"). Opposed to depressor.
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tic (n.)
twitching of a facial muscle, 1822, often a shortening of tic douloureux "severe facial neuralgia," literally "painful twitch" (1798), from French tic "a twitching disease of horses" (17c.), of unknown origin. Klein suggests an imitative origin; Diez compare it to Italian ticchio "whim, caprice, ridiculous habit," itself of unknown origin.
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