The root מזח appears three times in תנ”ך:

ישעיהו כג:י
עִבְרִ֥י אַרְצֵ֖ךְ כַּיְאֹ֑ר בַּת־תַּרְשִׁ֕ישׁ אֵ֖ין מֵ֥זַח עֽוֹד:

תהלים פרק קט פסוק יט
תְּהִי־ל֖וֹ כְּבֶ֣גֶד יַעְטֶ֑ה וּ֝לְמֵ֗זַח תָּמִ֥יד יַחְגְּרֶֽהָ:

איוב פרק יב פסוק כא
שׁוֹפֵ֣ךְ בּ֭וּז עַל־נְדִיבִ֑ים וּמְזִ֖יחַ אֲפִיקִ֣ים רִפָּֽה:

 According to Even-Shoshan, מזח has two meanings: (a) a bridge from the shore to the sea and (b) a belt.

Tawil suggests it is similar to the Akkadian mezehu, which means “sash”.  He further explains that a mezehu would be made of cloth, as opposed to a miserru which was made of leather.

The verse in Psalms clearly refers to an article of clothing that is worn around the waist.

HALOT has similar definitions.  In the case of Isaiah 23:10, a harbour, shipyard, or wharf, and in the other two cases, a waistband.