The crossword solution for the term 'MAD AS A HEN' is WET, which has three letters. This phrase is an idiom that is used to describe someone who is very angry or frustrated. It is derived from the behavior of a HEN when it is disturbed or threatened. The HEN will become agitated and flustered, often making loud noises and flapping its wings. This phrase is used to describe someone who is similarly agitated and frustrated.