An Idiom is is an expression, word, or phrase that has a figurative meaning that is comprehended in regards to a common use of that expression that is separate from the literal meaning or definition of the words of which it is made.
Mentira = Lie
Mentira piadosa : when you lie to somebody for pity or compassion.
Mentira oficiosa: when you lie with the purpose to be liked by someone.
Coger a alguien en mentira: to catch somebody lying.
Decir mentira por sacar verdad or sacar verdad por mentira : to pretend to know something with the purpose to make another person who really knows to talk about it.
Parece mentira. to denote surprise, this is incredible!
Please feel free to discuss further or add new Idioms using the same word.