There are a number of words that can be used as synonyms for the term "fanatical." Some of these include zealous, passionate, enthusiastic, fervent, ardent, obsessed, and extreme. Each of these words carries a slightly different connotation, but all share the sense of strong devotion or belief. Zealous implies a high degree of devotion or dedication, while passionate suggests intense emotion or feeling. Fervent, ardent, and obsessed all imply a deep and almost overwhelming commitment or preoccupation. Finally, extreme connotes a level of intensity that goes beyond what might be considered reasonable or normal. All of these synonyms can be used to describe someone who is highly dedicated or committed to a particular cause, belief, or interest.