The footnotes for 1 Tim 3:1 in The Ignatious Catholic Study Bible says:
Bishop: An overseer or spiritual shepherd who carries on the mission of the origional Apostles. Note that the titles “bishop” and “elder/presbyter” were somewhat fluid in the early years of the Church, and it seems that they could be used interchangeably (Tit 1:5-7; Acts 20:17,28). Soon, however, the distinction between bishops (1 Tim 3:1), elders (5:17), and deacons (3:8) was clearly defined and their respective titles were standardized.
