Excessive enthusiasm, unreasoning zeal, or wild and extravagant notions, on any subject, especially religion; religious frenzy
disapproval Fanaticism is fanatical behaviour or the quality of being fanatical. a protest against intolerance and religious fanaticism. = extremism. extreme political or religious beliefs - used to show disapproval = extremism
a person motivated by irrational enthusiasm (as for a cause); "A fanatic is one who can't change his mind and won't change the subject"--Winston Churchill
If you say that someone is a fanatic, you mean that they are very enthusiastic about a particular activity, sport, or way of life. Both Rod and Phil are football fanatics. = enthusiast
Pertaining to, or indicating, fanaticism; extravagant in opinions; ultra; unreasonable; excessively enthusiastic, especially on religious subjects; as, fanatic zeal; fanatic notions
disapproval If you describe someone as a fanatic, you disapprove of them because you consider their behaviour or opinions to be very extreme, for example in the way they support particular religious or political ideas. I am not a religious fanatic but I am a Christian. = extremist