What does "put someone up for something" mean? Is it an idiom?
To put someone or something up means to place someone somewhere. The phrase "put up" is not usually used for people, except in this context of adoption. When a child is given away for someone else to adopt the phrasal verb "put up" is used to describe this action. However, "put up" is normally used for objects and there are very few contexts besides adoption where "put someone up" is used. Ex: My birth parents put me up for adoption when I was two years old.