Metheg-ammah

bridle of the mother, a figurative name for a chief city, as in (2Sam 8:1 ), "David took Metheg-ammah out of the hand of the Philistines" (R.V., "took the bridle of the mother-city"); i.e., subdued their capital or strongest city, viz., Gath (1Chr 18:1).

EBD - Easton's Bible Dictionary