The Word "Priest"

The Greek word for "priest" is "hiereus."  (It shows up in the English word "hierarchy.")  In the New Testament, "hiereus" is used of pagan priests, Jewish priests, and Jesus Christ.  It is never used of Christian ministers.

Christian ministers in the New Testament fall into three categories:

• deacon (the Greek "diakonos" means "servant")
• presbyter or elder (the Greek "presbyteros" means "elder")
• bishop (the Greek for "bishop" is "episkopos," whose literal meaning is "overseer")

The New Testament's presbyters/elders were the equivalent of the people we today call "priests."  Over time, the word "presbyter" morphed into our word "priest."  Soon enough, priests came to be considered a sacred caste, etc., etc.

For the full story -- I've oversimplified it horrifically -- see Paul Dinter, The Changing Priesthood.