adj. 25B6; adjective
they are fanatical about their faith : ZEALOUS, extremist, extreme, militant, dogmatic, radical, diehard; intolerant, single-minded, blinkered, inflexible, uncompromising.
he was fanatical about tidiness : ENTHUSIASTIC, eager, keen, fervent, ardent, passionate; obsessive, obsessed, fixated, compulsive; informal wild, gung-ho, nuts, crazy; Brit. informal potty.