rock 1 
(rŏk)
(rŏk)n.
Idioms: 1. Relatively hard, naturally formed mineral or petrified matter; stone.
2.
a. A relatively small piece or fragment of such material.
b. A relatively large body of such material, as a cliff or peak.
3. A naturally formed aggregate of mineral matter constituting a significant part of the earth's crust.
4. One that is similar to or suggestive of a mass of stone in stability, firmness, or dependability: The family has been his rock during this difficult time.
5. rocks Slang Money.
6. Slang A large gem, especially a diamond.
7. Slang Crack cocaine.
8.
a. A varicolored stick candy.
b. Rock candy.
between a rock and a hard place
Confronted with equally unpleasant alternatives and few or no opportunities to evade or circumvent them.
on the rocks
1. In a state of difficulty, destruction, or ruin: Their marriage is on the rocks.
2. Without money; bankrupt: Our accountant says the business is on the rocks.
3. Served over ice cubes: Scotch on the rocks.
[Middle English, from Old North French roque, from Vulgar Latin *rocca, of unknown origin .]