Idioms Using FOR

Adverb for a relatively small amount of money
for a song
Some newlyweds are delaying or eschewing home buying. Many young families have parents with large houses — bought for a song in cheaper, more booming times — with plenty of room to share.
Phrase even though it may not be important or valuable
Visitors to a zoo in China got a rude surprise when the lion began to bark. In fact it was no lion, but just a Tibetan mastiff, which, for what it's worth, looks more like the king of the jungle than perhaps any other canine.
Noun disorganized fight or event in which everyone present takes part
A group of 40 people in Germany had gathered to toss snowballs at each other but the game quickly degenerated into a massive free-for-all that required police intervention.
Adjective has a natural ability or tolerance to do something
This 29-year-old has a head for heights and has been honing his death-defying skills since the age of five, with circus troupes around the globe.
Phrase will be happy with what is about to happen
in for a treat
If you’ve never made pinwheels before, you’re in for a treat! I love how quick and cute they are. They’re the perfect addition to your summer decor and they look impressive while taking no time at all to create.
Phrase something that will be remembered for a long time
one for the ages
NASA's Mars rover has made it's first major discovery, and it's one for the ages. Water once coursed over the now bone-dry surface, a finding based on the presence of rounded pebbles and gravel near the rover's landing site.
Phrase prepare for and simplify progress of something
paving the way for
German researchers have examined the ability of nano-sized gold particles to melt lipid membranes surrounding cells, paving the way for dissolving sick cells and curing cancer.
Verb show support for
Carrying the mantle of the legendary luchador Blue Demon, he sees his role as part of a larger mission to speak up for Mexican immigrants. His feud with Oliver John is an allegory for the political battles being fought today.
Phrase underestimate the value of
Throwing a bottle of water to a friend or pitching a baseball is probably something most of us take for granted. But accurate throwing is something that evolutionary biologists suspect may be exceptional to our species.
Phrase situation in which you do something to harm someone who has done something harmful to you
tit for tat
The camel asked the fox, ‘Are you sorry you were so selfish and caused me to be beaten by the farmer?’ ‘Yes, yes!’ cried the fox. ‘And I am sorry I had to teach you a lesson --many times in life it is a case of tit for tat.'