🔼The name Baalis in the Bible
The name Baalis occurs only one time in the Bible. The prophet Jeremiah tells the story of how Johanan, son of Kareah, visits vassal Gedaliah, son of Ahikam, at Mizpah and tells him that Baalis, king of the Ammonites has sent Ishmael, son of Nethaniah, to kill him. And if he should go and knock off Ishmael before he can act. But Gedaliah doesn't buy Johanan's story and tells him not to do anything (Jeremiah 40:14).
🔼Etymology of the name Baalis
At second glance, however, there's nothing in the Hebrew language that can account for the -is part. It may be that the יס is a scribal error for ים, forming a common plural: Ba'alim, meaning Lords. But that's not very likely.
It's more likely that the name Baalis was formed from a contraction of two elements, the first of them being the common noun בן (ben), meaning son:
The second part of the name Baalis then might come from a small cluster of adjacent root-verbs that includes the verb עלס (alas), meaning to rejoice:
Hence the name בעליס (Baalis) would be a contraction of בן־עליס (Ben-aliys).
For a meaning of the name Baalis, Jones' Dictionary of Old Testament Proper Names suggests Son Of Exultation. BDB Theological Dictionary reads Son Of Delight. NOBSE Study Bible Name List doesn't propose a translation.