The name Melchizedek in the Bible
Melchizedek is the king of Salem and priest of El Elyon (Genesis 14:18). He has a small but far stretching role in the War of Four against Five Kings, in the aftermath of which Abraham's nephew Lot is abducted by the survivors of that war and subsequently freed by Abraham and his coalition.
Since these stories were (apart from divinely inspired) based on oral traditions, glossed with verifiable facts, and written in their present form in Babylon, the story in which Abraham beats the vast armies of the Mesopotamian alliance with 318 good old boys and takes home his kin (Genesis 14:14), is quite openly an allusion to the return from Babylonian exile and the restoration of the temple and worship of YHWH.
Melchizedek gives Abraham bread and wine and blesses him, and Abraham gives Melchizedek a tenth of the goods that he retrieved from the looters. This action gave rise to the law of tithing (via Genesis 28:22, via Leviticus 27:30 to Deuteronomy 14:22-29; also see Hebrews 7:1-10).
King David seems to have access to Scriptures (or direct revelation) that are lost to us when he cites God in Psalm 110:4, "You are a priest forever, according to the order of Melchizedek." That there used to be a strong tradition about this Melchizedek becomes evident in Paul's letter to the Hebrews (Hebrews 5:6, 5:10, 6:20 etc). In this sense there is a huge difference between Melchizedek and Jethro, another famous priest, although at first he is perhaps not a priest of the God of Israel. Jethro is the father of Zipporah, the first wife of Moses, whose allegiance to God becomes evident only after he sees the success of Israel (Exodus 18:11).
In the Greek New Testament the name Melchizedek is spelled Μελχισεδεκ (Melchisedek).
Etymology of the name Melchizedek
The use of a hyphen in a name is quite unusual, and although Melchizedek seems a personal name, it looks more like a title. It consists of two elements, the first one taken from the noun מלך (melek), meaning king:
The letter י is possessive, and the form מלכי means either my king, or king of.
The second part of the name Melchizedek comes from the verb צדק (sadeq), meaning to be just:
Jones' Dictionary of Old Testament Proper Names and NOBSE Study Bible Name List agree on the meaning of Melchizedek: King Of Righteousness. BDB Theological Dictionary sees in the zedek-part a reference to someone (some god?) named Sedeq, and reads My King Is Sedeq.