In the eighteenth year of King Jeroboam

This refers to the eighteenth year of Jeroboam's reign as king. Alternate translation: "In the eighteenth year that Jeroboam was king" or "in year 18 of King Jeroboam's reign" (See: rc://en/ta/man/jit/figs-explicit and rc://en/ta/man/jit/translate-ordinal)