In her effort to conform NT pastors to her erroneous understanding of the Lord's Supper (“Eucharist”), Catholicism came to render presbuteros” as “priests” (which the RC Douay Rheims Bible inconsistently does: Acts 20:17; Titus 1:5), and sometimes “episkopos,” in order to support a distinctive NT sacerdotal priesthood in the church, but which the Holy Spirit never does. For the word which the Holy Spirit distinctively uses for priests*, is “hiereus” or “archiereus.” (Heb. 4:15; 10:11) is never used for NT pastors. Nor do the words presbuteros (senior/elder) or episkopos (superintendent/overseer) - which He does use for NT pastors - mean "priest." Presbuteros or episkopos do not denote a unique sacrificial function, and hiereus (as archiereus=chief priests) is used in distinction to elders in such places as Lk. 22:66; Acts 22:5.
What occurred is that "presbuteros" in Greek (presbyter in Latin) was translated into English as "preost," and then "priest," but which also became the word used for "hierus" ("sacerdos" in Latin), losing the distinction the Holy Spirit made by never distinctively giving NT presbuteros the distinctive title hiereus.
Jewish elders (Hebrew "zaqen") as a body existed before the priesthood of Levitical priests (Hebrew "kohen"), most likely as heads of household or clans, and being an elder did not necessarily make one a Levitical priest (Ex. 3:16,18, 18:12; 19:7; 24:1; Num. 11:6; Dt. 21:2; 22:5-7; 31:9,28; 32:7; Josh. 23:2; 2Chron. 5:4; Lam. 1:9; cf. Mt. 21:13; 26:47) or a high priest, offering both gifts and sacrifices for sins. (Heb. 5:1) While elders exercise could some priestly functions such as praying and laying hands on sacrifices, yet unlike presbuteros and episkopos, elders and priest were not the same in language or in function. Like very young Samuel, one could be a kohen/priest without being an zaqen/elder, and one could be a elder without formally being a priest, whose primary function was to offer expiatory sacrifices for the people. It is also understood that even the Latin word "sacerdos" which corresponds to priest has no morphological or lingual relationship with the Latin word for “presbyter.”
All believers are called to sacrifice (Rm. 12:1; 15:16; Phil. 2:17; 4:18; Heb. 13:15,16; cf. 9:9) and all constitute the only priesthood (hieráteuma) in the NT church, that of all believers, (1Pt. 2:5,9; Re 1:6; 5:10; 20:6). But nowhere at NT pastors distinctively titled hiereus, and the idea of the NT presbuteros being a distintive class titled "hiereus" was a later development, due to imposed functional equivalence, supposing NT presbyteros engaged in a unique sacrificial ministry as their primary function.
Catholic writer Greg Dues in "Catholic Customs & Traditions, a popular guide," states, "Priesthood as we know it in the Catholic church was unheard of during the first generation of Christianity, because at that time priesthood was still associated with animal sacrifices in both the Jewish and pagan religions." "When the Eucharist came to be regarded as a sacrifice [after Rome's theology], the role of the bishop took on a priestly dimension. By the third century bishops were considered priests. Presbyters or elders sometimes substituted for the bishop at the Eucharist. By the end of the third century people all over were using the title 'priest' (hierus in Greek and sacerdos in Latin) for whoever presided at the Eucharist." (http://books.google.com/books?id=ajZ_aR-VXn8C&source=gbs_navlinks_s) And R. J. Grigaitis (O.F.S.) (while yet trying to defend the use of priest), reveals, "The Greek word for this office is ‘?e?e?? (hiereus), which can be literally translated into Latin as sacerdos. First century Christians [such as the inspired writers] felt that their special type of hiereus (sacerdos) was so removed from the original that they gave it a new name, presbuteros (presbyter). Unfortunately, sacerdos didn't evolve into an English word, but the word priest [from old English "preost"] took on its definition." (http://grigaitis.net/weekly/2007/2007-04-27.html)
In response to a query on this issue, the web site of International Standard Version (not my preferred translation) states, No Greek lexicons or other scholarly sources suggest that "presbyteros" means "priest" instead of "elder". The Greek word is equivalent to the Hebrew ZAQEN, which means "elder", and not priest. You can see the ZAQENIM described in Exodus 18:21-22 using some of the same equivalent Hebrew terms as Paul uses in the GK of 1&2 Timothy and Titus. Note that the ZAQENIM are NOT priests (i.e., from the tribe of Levi) but are rather men of distinctive maturity that qualifies them for ministerial roles among the people. Therefore the NT equivalent of the ZAQENIM cannot be the Levitical priests. The Greek "presbyteros" (literally, the comparative of the Greek word for "old" and therefore translated as "one who is older") thus describes the character qualities of the "episkopos". The term "elder" would therefore appear to describe the character, while the term "overseer" (for that is the literal rendering of "episkopos") connotes the job description. To sum up, far from obfuscating the meaning of "presbyteros", our rendering of "elder" most closely associates the original Greek term with its OT counterpart, the ZAQENIM. ...we would also question the fundamental assumption that you bring up in your last observation, i.e., that "the church has always had priests among its ordained clergy". We can find no documentation of that claim. ( http://isvbible.com/catacombs/elders.htm) The Catholic titular use of hiereus/priest for presbyteros/elder is defended by the use of an etymological fallacy , since "priest" from old English "preost" etymologically is derived from "presbyteros," due to imposed functional equivalence, supposing NT presbyteros engaged in a unique sacrificial ministry as their primary function.
Etymology is the study of the history of words, their origins, and evolving changes in form and meaning. over time, however, etymologies are not definitions. The etymological fallacy here is a linguistic misconception, a genetic fallacy that erroneously holds that the present-day meaning of a word or phrase should necessarily be similar to or the same as its original or historical meaning. So that since presbyteros incorrectly became priest from preost, therefore it is erroneously considered to be valid to use the same title for OT priests as for NT pastors, due to imposed functional equivalence, supposing that the presbyters engaged in a unique and primary sacrificial function of turning bread and wine into the physical body and blood of Christ as an expiation for sins, and which is then physically consumed to gain spiritual and eternal life. But instead of dispensing bread as part of their ordained function, which NT pastors are never described as doing in the life of the church, and instead the primary work of NT pastors is that of prayer and preaching. (Act 6:3,4) "Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine." (2 Timothy 4:2) And which is what is said to "nourish" the souls of believers, and believing it is how the lost obtain life in themselves. (1 Timothy 4:6; Psalms 19:7;Acts 15:7-9) Thus distinctively identifying Christian clergy with the same distinctive title used for the Jewish sacerdotal clergy (priests) rather than the term the Holy Spirit calls these pastors (presbyters/elders) is unscriptural and functionally unwarranted. Nor is the church shown making this Catholic eucharist an atonement for sin and the practice around which all else revolves as in Catholicism, and instead the only teaching in Acts and onward (which interprets the gospels) that manifestly describes the supper to any real extent is that of 1 Cor. 11:17-34, and in which the church is the body of Christ, which is to "show (declare, proclaim) the Lord's death" for the church by treating each other as members of that body which in unity with Him, in communally taking part in the "feast of charity," (cf. Jude. 1:12) unselfishly sharing bread and the blood of grapes (preferably) with each other, which Christ supremely showed in purchasing the church with His sinless shed blood. (cf. Acts 20:28)
Have we got to the knockdown; dragout stuff yet?