|Easton's Bible Dictionary|
Bridle of the mother, a figurative name for a chief city, as in 2 Samuel 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 Chronicles 18:1).
Int. Standard Bible Encyclopedia
me-theg-am'-a, meth-eg-am'-a (mathegh ha-'ammah, "bridle of the metropolis"; Septuagint ten aphorismenen): It is probable that the place-name Metheg-Ammah in 2 Samuel 8:1 the King James Version should be rendered as in the Revised Version (British and American), "the bridle of the mother city," i.e. Gath, since we find in the parallel passage in 1 Chronicles 18:1 gath ubhenotheha, "Gath and her daughters," i.e. daughter towns. The Septuagint has an entirely different reading: "and David took the tribute out of the hand of the Philistines," showing that they had a different text from what we now have in the Hebrew. The text is evidently corrupt. If a place is intended its site is unknown, but it must have been in the Philistine plain and in the vicinity of Gath.
Methegammah (1 Occurrence)
2 Samuel 8:1 And after this it came to pass that David smote the Philistines, and subdued them: and David took Methegammah out of the hand of the Philistines. (KJV)