Easton's Bible Dictionary (1897)
Bridle of the mother, a figurative name for a chief city, as in 2 Sam. 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 (1 Chr. 18:1).
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
ME'THEG-AM'MAH (curb of the metropolis). This word, in 2 Sam 8:1, is translated in the margin "the bridle of Ammah," and it may be rendered "the bridle or bit of the metropolis," meaning that David subdued the metropolis of the Philistines, probably Gath. Thus expressed, the passage corresponds closely with the parallel passage, 1 Chr 18:1: "Gath and her towns."
Hitchcock's Bible Names (1869)
bridle of bondage