🔼The name Ader in the Bible
The name Ader is spelled identical to the name Eder but (according to the Masoretes) was pronounced slightly different. The difference is so small, though, that most modern translations don't even list different names and read Eder for all.
Most traditional translations, however, list Ader among the sons of Beriah of Benjamin, a family-head living in Aijalon, who chased off the indigenous population of the Philistine city of Gath, where Goliath was from (1 Chronicles 8:15).
🔼Etymology of the name Ader
The name Ader comes from the root group עדר (adar I, II & III):
It's not obvious which of the root-verbs yields our name but most of the commentators go with עדר III.
For a meaning of the name Ader, Jones' Dictionary of Old Testament Proper Names reads Flock. BDB Theological Dictionary doesn't translate our name but refers to a cognate Arabic root meaning Loitering or Lagging. NOBSE Study Bible Name List doesn't list Ader separately but lists four Eders and translates this name with A Flock.