1. A rock immediately adjacent to a vein or fault

Derived forms: wall rocks

Type of: rock, stone

• on tap
• on tenterhooks
• on that
• on that point
• on the average
• on the ball
• on the button
• on the coattails
• on the contrary
• on the dot
• on the face of it
• on the fence
• on the fly
• on the go
• on the hook
• on the house
• on the level
• on the line
• on the loose
• on the mend
• on the nail
• on the nose
• on the off chance
• on the offensive
• on the one hand