Specialty priest

A speciality priest was a special kind of priest of a deity.

Difference from other Clerics
Speciality priests and clerics were the same in the sense of both being practitioners of divine magic. The diffeerence lay in their level of dedication to one deity. A cleric worshipped an entire pantheon, possibly praising one member of the pantheon above the rest, -maybe even disagreeing with the rest- whereas a speciality priest was a follower of only one specific deity.

Differences in Powers
The options of powers possessed by every cleric was very varied. This was because the cleric was offered a huge variety of powers from every member of his pantheon. A speciality priest was limited in his choices even to the point of forfeiting some like the ability to turn undead. In return, a speciality priest gained specific powers from his specific deity, that starkley differed from those of a standard cleric.

Difference in Reception
A cleric was - at least in theory - respected and liked by the entire pantheon, both by its members and priests thereof, except by those members of a pantheon who were opposed to each other. A speciality priest on the other hand was poorly received from other members of a pantheon, than the one he or she worshiped, and by their followers, of course exceptions existed.