🔼The name Jazer in the Bible
Jazer (or Jaazer, as some translations have it) was a city east of the Jordan, near Aroer and the mountains of Gilead (2 Samuel 24:5, 1 Chronicles 26:31). At the time of the conquest of Canaan, Jazer and its satellite villages were occupied by Amorites, but they were dispossessed by a reconnaissance contingent that Moses had sent out (Numbers 21:32).
The lands surrounding Jazer were most suitable for sustaining large amounts of life stock, and the tribes of Reuben and Gad made claim to it. Moses reminded them that YHWH decreed all of Israel to settle west of the Jordan, but Reuben and Gad wanted what they had their minds set on. They nevertheless promised to cross the Jordan and help the rest of Israel conquer Canaan (Numbers 32).
When the lands were more precisely divided, Jazer and environs came to be situated in the territory allotted to the tribe of Gad (Joshua 13:25). Later Jazer itself was assigned to the Merarite Levites (Joshua 21:39).
Much later, the tribes of Reuben and Gad experienced why the Lord wanted them on the west of the Jordan, because when the Assyrians started their conquest, Reuben and Gad were among the first to be picked off. Both prophets Isaiah and Jeremiah elaborated on Jazer's fall in their prophecies against Moab (Isaiah 16:8-9, Jeremiah 48:32).
In 1 Chronicles this name is spelled with an additional yod: יעזיר (Jazir). In Numbers 21:24 occurs the word עז, which only the NAS appears to take as a truncated version of Jazer, and all other translation as, well, the word עז ('az), meaning strong or strength.
🔼Etymology of the name Jazer
The name Jazer comes from the root-verb עזר (azar), meaning to help or support:
The name Jazer looks like a common expression of the verb עזר (azar), and would mean He Shall Help. For a meaning of the name Jazer, NOBSE Study Bible Name List proposes a descriptive Helpful. Jones' Dictionary of Old Testament Proper Names proposes a rather overly elaborate Whom The Lord Helps (our name does not contain a reference to YHWH). BDB Theological Dictionary doesn't offer an interpretation of our name but does list it under the verb עזר (azar).