1 a [noncount] : the hard, solid material that the surface of the Earth is made of
▪ They drilled through several layers of solid rock. ▪ Moss can grow on bare rock. ▪ The miners made a tunnel through the rock. ▪ volcanic rock — often used before another noun ▪ The mountain had many amazing rock formations. — see also bedrock, sheetrock
b [count] : a piece of rock
▪ a flat rock ▪ (US) We threw rocks [=stones] into the water. ▪ a pile of rocks
c [count] : a large piece of rock that sticks up from the surface of the Earth
▪ She climbed the rock. ▪ The ship crashed into the rocks. 2 — used in phrases to say that something is very hard, steady, etc. ▪ This bread is (as) hard as a rock. = The bread is rock-hard. [=the bread is very hard] ▪ Her hand was steady as a rock. [=her hand was very steady] ▪ His muscles are solid as a rock. [=very strong/solid] ▪ The frozen chicken is rock-solid. ▪ The beat of the drum was rock-steady. 3 [singular] informal a : a strong person who can be relied on
▪ We could always count on him—he was our rock.
b : someone whose ideas, values, ways of doing things, etc., do not change
▪ Once she makes up her mind, she's (like) a rock. [=nobody can change her mind once she decides something] 4 [count] informal : a diamond or other jewel
▪ Look at the size of that rock on her finger. 5 [noncount] Brit : hard candy that is made in a stick
▪ a stick of rock — compare rock candy 6 [count] informal : a small hard piece of a drug
▪ a rock of crack cocaine