From an unused root meaning to be slender; properly, the waist or small of the back; only in plural the loins -- + greyhound, loins, side.
מָתְנַ֫יִם noun masculine dual loins (Arabic back, the two sides of the back, etc.; Syriac ; — absolute ׳מ Deuteronomy 33:11 7t., מָתְנָ֑יִם Ezekiel 29:7; 47:4; construct מָתְנֵי Jeremiah 13:11 + 3t.; suffix מָתְנַי Isaiah 21:3, מָתְנָ֑י Jeremiah 13:2; מָתְנֵיהֶם 1Kings + Jeremiah 20:32 4t., etc.; — loins:
b. hence place of things attached to girdle: — sword girded on (אסר על, חגר 2 Samuel 20:8; Nehemiah 4:12; opposed to, אֲפַתֵּחַ מְלָכִים וּמָתְנֵי Isaiah 45:1 and the loins of kings I will loosen, i e. will disarm them (׳י before Cyrus; compare Che); ink-horn Ezekiel 9:2-3, 11.
d. מ ׳זַרְזִיר Proverbs 30:31 that which is girt in the loins, i.e. probably either a greyhound Ew Bö De (contracted, as if by a belt), or a war-horse, charger, Bo Ges Hi Str Wild (with a saddle); compare also זרזיר, p. 267 above; text perhaps corrupt (Wild).
f. linen breeches of priests were to extend יְרֵכַיִם וְעַד מִמָּתְנַיִם Exodus 28:42 (P); to be ׳עַלמָֿת Ezekiel 44:18; loins of slaves are girt with waistcloth, compare Job 12:18 (see also אֵזוֺר).
2. a. loins as seat of strength, Deuteronomy 33:11; 1 Kings 12:10 2 Chronicles 10:10; מָתְנַיִם חַזֵּק Nahum 2:2 ("" כֹּחַ אַמֵּץ); בְּמָתְנָיו כֹּחוֺ Job 40:16 (of hippopotamus); in combination with 1a (figurative) מ ׳בְּעוֺז חָֽגְרָה Proverbs 31:17 she girdeth her loins with strength, she puts on energy with her girdle; compare also מ ׳בְּשִׁבְרוֺן Ezekiel 21:11 sigh with breaking of loins, i.e. in entire collapse of strength; so וּמ ׳הַמְעַ֑ד תָּמִיד Psalm 69:24 and make their loins continually to shake, make them totter; compare Ezekiel 29:7 (where read וְהִמְעַדְתָּ for וְהַעֲמַדְתָּ, see מָעַד).