Etymology
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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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pectoral (n.)

early 15c., "ornament worn on the breast," from Old French pectoral and directly from Latin pectorale "breastplate," noun use of neuter of adjective pectoralis (see pectoral (adj.)). Related: Pectorally. As a shortened form of pectoral muscle, attested from 1758. Slang shortening pec for this is first recorded 1966. Related: Pectorals; pecs.

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psoas (n.)

muscle in the loins or pelvis, 1680s, from Greek psoa (plural psoai) "muscles of the loins." Related: Psoitis; psoitatic.

Gk. [psoas], the gen. of the feminine noun [psoa], was mistaken by the French anatomist Jean Riolan (1577-1657) for the nom. of a (nonexistent) masculine noun. It was he who introduced this erroneous form into anatomy. [Klein]
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abdominal (adj.)

"pertaining to the abdomen, ventral," 1550s, from medical Latin abdominalis, from abdomen (genitive abdominis); see abdomen. As a noun, "abdominal muscle," by 1961 (earlier "abdominal vein," 1928);  earlier as a fish of the order including carp, salmon, and herring (1835), so called for their ventral fins. Related: Abdominally. English in 17c. had abdominous "big-bellied."

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lizard (n.)

"an animal resembling a serpent, with legs added to it" [Johnson], late 14c., lusarde, from Anglo-French lusard, Old French laisarde "lizard" (Modern French lézard), from Latin lacertus (fem. lacerta) "lizard," a word of unknown origin. The ending in French and English is probably influenced by words in -ard.

It is identical to Latin lacertum "upper arm, muscular part of the arm, from the shoulder to the elbow" (opposed to bracchium), which suggests a pattern similar to that of Latin musculus "a muscle," literally "little mouse" (diminutive of mus "mouse"), so called because the shape and movement of the biceps were thought to resemble mice. It is unclear which Latin sense, the arm-muscle or the lizard, is original. De Vaan finds the words perhaps connected to Greek likertizein "to jump, dance," which Beekes finds likely from Pre-Greek.

Run fast, stand still. This, the lesson from lizards. [Ray Bradbury]
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