Mariah Carey's nickname is MIMI, which is a four-letter word. Mariah Carey is an American singer, songwriter, actress, and record producer who has had a successful career in the music industry since the 1990s. She is known for her five-octave vocal range, melismatic singing style, and signature use of the whistle register. Her nickname, MIMI, was given to her by her mother when she was a child and has stuck with her ever since.