if there is a nip in the air, the air is cold.

There's quite a nip in the air. I think you'll need your jacket on.

• be as bright as a button
• be as brown as a berry
• be as busy as a bee
• be as clean as a whistle
• be as clear as crystal
• be as clear as day
• be as clear as mud
• be as cold as ice
• be as cool as a cucumber
• be as crazy as they come
• be as [crazy/rich etc.] as they come
• be as cute as a button
• be as daft as a brush
• be as dead as a dodo
• be as dead as a doornail
• save your bacon
• save your breath
• save your own skin
• saving grace
• savoir-faire
• say a lot about
• say a lot about something
• say boo
• Say cheese!
• say enough is enough