give (someone) a heads up

to give someone information or a warning.

I wanted to give you a heads up that I'll be sending you the revised form for your approval.

Usage notes: sometimes used in the form get a heads up:

They promised we'd get a heads up on the new proposal tomorrow.

• the world is your oyster
• the worm has turned.
• the worse for wear
• the worst-case scenario
• the worst of both worlds
• the writing is on the wall
• the writing on the wall
• the wrong side of the tracks
• They broke the mould when they made someone.
• They broke the mould when they made something.
• They can whistle for it!
• thick skin
• thick-skinned
• thin end of the wedge
• thing is
• thing of the past
• thing or two
• things have come reached a pretty pass
• things have come to a pretty pass
• think again
• think are God's gift to women
• think back
• think better of
• think better of it
• think better of something