Rashi on Deuteronomy 3:4/רש"י על דברים ג׳:ד׳

1חבל ארגב [ALL] THE LINE OF ARGOB — We render this in the Targum by בית פלך טרכונא Now I have seen that the Jerusalem Targum of the Scroll of Esther terms a palace טרכונין. I learn from this that חבל ארגב signifies “the province of the Royal Palace”, denoting that the province is called after its name (after the name of the palace). Similarly, also the term ארגוב found in the Book of Kings (2 15:25) where the meaning is that Pekah the son of Remaliah slew Pekahia the son of Menahem near the king’s palace (את ארגוב), I learn that thus (after the palace) was the province named.