rock (n.1)

[stone, mass of mineral matter], Middle English rokke, roche "stone as a substance; large rocky formation, rocky height or outcrop, crag," from Old English rocc (as in stanrocc "stone rock or obelisk") and directly from Old North French roque, variant of Old French roche, which is cognate with Medieval Latin rocca (8c.), from Vulgar Latin *rocca, a word of uncertain origin. According to Klein and Century Dictionary, sometimes said to be from Celtic (compare Breton roch). Diez suggests Vulgar Latin *rupica, from Latin rupes "rocks."

In Middle English it seems to have been used principally for large rock formations but occasionally of individual boulders. The extended sense of "a stone of any size" is by 1793, American English colloquial, and long was considered incorrect.

It is an error to use rock for a stone so small that a man can handle it : only a fabulous person or a demi-god can lift a rock. [Century Dictionary]

The meaning "precious stone," especially a diamond, is by 1908, U.S. slang; the sense of "crystallized cocaine" is attested from 1973 in West Coast slang. Also used attributively in names of animals that frequent rocky habitats, as in rockfish, rock badger, rock lobster (the last attested by 1843).

Rock is used figuratively for "a sure foundation, something which gives one protection and security" (especially with reference to Christ), from the 1520s (Tyndale); but it also has been used since the 1520s as "cause or source of peril or destruction," an image from shipwrecks.

Between a rock and a hard place "beset by difficulties with no good alternatives" is attested by 1914 in U.S. Southwest:

to be between a rock and a hard place, vb. ph. To be bankrupt. Common in Arizona in recent panics; sporadic in California. [Dialect Notes, vol. v, part iv, 1921]

As an example of fine distinctions, a party of men were discussing the present situation of the German army, this week. One remarked that the Germans were between the devil and the deep sea; while another corrected him by saying that the Germans were between the upper and nether mill stone. The third man whose name is Pilgreen, and who works in the treasurer's office, simply remarked that the Germans were between a rock and a hard place. [local item in the Pouteau (Oklahoma) Weekly Sun,  Oct. 1, 1914]

The rock-scissors-paper game is attested by that name by 1976 (as paper stone and scissors by 1941). Sources agree it is based on Japanese Jan Ken Po or Jan Ken Pon (or Janken for short); the Japanese game is described in English publications by 1879.

rock (v.1)

[to sway, move backward and forward] Middle English rokken "rock (a cradle), cause to sway back and forth; rock (someone) in a cradle," from late Old English roccian "move a child gently to and fro" in a cradle, which is related to Old Norse rykkja "to pull, tear, move," Swedish rycka "to pull, pluck," Middle Dutch rucken, Old High German rucchan, German rücken "to move jerkily."

The intransitive sense of "move or sway back and forth unstably" is from late 14c. For the popular music senses, see rock (v.2). Related: Rocked; rocking.

The earliest associations of the word were with slumber, rest, security. The sense of of "sway to and fro under some impact or stress" is from late 14c., especially of vessels in the waves (1510s); hence rock the boat in the figurative sense "stir up trouble" (1914). The sense of "swing to and fro in or as in a rocking chair" is by 1795.

rock (v.2)

"to dance to popular music with a strong beat," 1948 (in song title "We're gonna rock"), from rock (v.1) in an earlier blues slang sense of "cause to move with musical rhythm" (1922); often used at first with sexual overtones, as in the 1922 song title "My Man Rocks Me (with One Steady Roll)". The sense developed in early 1950s to "play or dance to rock and roll music." Also see rock (n.2). Related: Rocked; rocking.

In reference to music, by 1938 as "to have a rocking rhythm;" by 1977 as "exhibit the characteristics of rock music." To rock out "enjoy oneself to rock music" is by 1968. Rocksteady, Jamaican pop music style (precursor of reggae), is attested from 1969.

rock (n.2)

1823, "action of rocking; a movement to and fro," from rock (v.1). As short for rock and roll, by 1957; but the sense of "musical rhythm characterized by a strong beat" is from 1946, in blues slang (Mezz Mezzrow, "Really the Blues"). Rock star is attested by 1966.

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Definitions of rock from WordNet
rock (n.)
a lump or mass of hard consolidated mineral matter;
he threw a rock at me
Synonyms: stone
rock (n.)
material consisting of the aggregate of minerals like those making up the Earth's crust;
that mountain is solid rock
Synonyms: stone
rock (n.)
(figurative) someone who is strong and stable and dependable; "Thou art Peter, and upon this rock I will build my church"--Gospel According to Matthew;
he was her rock during the crisis
rock (n.)
hard bright-colored stick candy (typically flavored with peppermint);
Synonyms: rock candy
rock (n.)
a genre of popular music originating in the 1950s; a blend of black rhythm-and-blues with white country-and-western;
rock is a generic term for the range of styles that evolved out of rock'n'roll.
Synonyms: rock 'n' roll / rock'n'roll / rock-and-roll / rock and roll / rock music
rock (n.)
pitching dangerously to one side;
Synonyms: careen / sway / tilt
rock (v.)
move back and forth or sideways;
She rocked back and forth on her feet
the ship was rocking
Synonyms: sway / shake
rock (v.)
cause to move back and forth;
rock the cradle
rock the baby
Synonyms: sway
Rock (n.)
United States gynecologist and devout Catholic who conducted the first clinical trials of the oral contraceptive pill (1890-1984);
Synonyms: John Rock