be slow on the uptake - to be slow to understand new ideas.

Some of the games were quite complex but the children were very quick on the uptake.

• rack brains
• rack up
• rack up something
• rack your brain
• rack your brains
• rags-to-riches
• raining cats and dogs
• rain on parade
• rain on someone's parade
• rain or shine
• rainy day fund
• raise a few eyebrows
• raise a stink
• raise Cain
• raised eyebrows
• raise eyebrows
• raise game
• raise hackles
• raise hand against
• raise hand against someone
• raise hand to
• raise hand to someone
• raise hell
• raise its head
• raise its ugly head