Charles Ellicott Commentary Judges 1:13

"And Othniel the son of Kenaz, Caleb`s younger brother, took it: and he gave him Achsah his daughter to wife." — Judges 1:13 (ASV)

Othniel.Joshua 15:15–17. It is added here that he was Caleb’s younger brother. (See Judges 3:9.) The Hebrew may mean either that Othniel was "son of Kenaz and brother of Caleb" (in which case he married his niece), or "son of Kenaz, who was Caleb’s brother" (as in Jonadab, the son of Shimeah David’s brother, 2 Samuel 13:3), in which case Achsah was his cousin. The Masoretes, to whom we owe the punctuation, and other such details, of our Hebrew Scriptures, show by their pointing that they understood the words in the former sense.

But though Ben-kenaz may simply mean Kenezite (Joshua 14:6; Numbers 32:12), it is strange in that case that Othniel should never be called a son of Jephunneh. If he was a brother of Caleb’s, he must have lived to an extreme old age and have been an old man when he married Achsah. For the importance of Caleb’s family, see 1 Chronicles 27:15. The Rabbis identify Othniel with the Jabez who is so abruptly introduced in 1 Chronicles 4:9–10, and connect Achsah’s petition with the prayer recorded there; and they suppose that he founded the school of scribes at Jabez (1 Chronicles 2:55) and was a teacher of law to the Kenites.