1. likely to fail because of serious problems.

At the time, it seemed like capitalism was on the rocks.

It became clear that her 15-year marriage to David was on the rocks.

Usage notes: most often refers to relationships between people or organizations, as in the examples

2. with ice.

I'll have a whiskey and soda on the rocks.

Usage notes: used only to refer to alcoholic drinks

• do a number on someone
• do a number on something
• do any favours
• do anything by halves
• do a power of good
• do a roaring trade
• do a slow burn
• do away with
• do away with someone
• do away with something
• do a world of good
• do battle
• do battle with
• do battle with something
• do best
• do bidding
• do bit
• do by halves
• do credit to
• do credit to someone
• do damnedest
• do dirt
• do dirty work
• do double duty
• do double duty as