Cost (one) dear British verb phrase UK informal
To cause problems; to lead to serious consequences.
Mark killed the daughter of mafia boss 3 years ago, which cost him dear.
Kate's scandal cost her dear. Many film producers turned her down as the lead actress for their films.
An error in their calculations cost them dear when the boss checked all of last month's sales figures.
To punish someone or something harshly
Once something has been done, you can do nothing but face the consequences.
White lie
Act in a way that is likely to cause problems for you
A way of saying that something never or unlikely happens
It'll be a cold day in July when I can speak fluently Spanish.