Waist

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late Middle English: apparently representing an Old English word from the Germanic root of wax2.

wiktionary

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From Middle English waste, wast(“stature, waist”), from Old English wǣst, *wǣxt, from Proto-Germanic *wahstuz(“growth, development, stature, build”), from Proto-Indo-European *h₂weg-s-(“to multiply, increase”). Cognate with Middle High German wahst(“growth”), Danish vækst(“growth”), Swedish växt(“growth, development, size”), Icelandic vöxtur(“growth”), Gothic 𐍅𐌰𐌷𐍃𐍄𐌿𐍃( wahstus, “growth”). Related to Old English weaxan(“to grow, increase”). More at wax.

etymonline

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waist (n.)

late 14c., "middle part of the body," also "part of a garment fitted for the waist, portion of a garment that covers the waist" (but, due to fashion styles, often above or below it), probably from Old English *wæst "growth," hence, "where the body grows," from Proto-Germanic *wahs-tu- (source also of Old English wæstm, Old Norse vöxtr, Swedish växt, Old High German wahst "growth, increase," Gothic wahstus "stature," Old English weaxan "to grow" see wax (v.)), from PIE *wegs-, extended form of root *aug- (1) "to increase."