Here's what rhymes with prothough.
so though show tho fo foe ho ceux faut hoe sew soe vo sho zo no know go although low co flow slow snow throw row lo bo doe dough fro mo po ro toe wo woe thro tow yo beau goe jo ko beaux cho dau floe mow noe roe yeux rho stow throe sloe whoa doh schmo schmoe ago ratio blow grow pro glow overthrow quo overflow chateau crow hello bio nouveau uno rodeo tuo bro chateaux trousseau trow chapeau oleo kayo chapeaux fatso trousseaux borzoi romeo resew below radio plateau audio bestow folio forego forgo polio propos aglow dicho escrow siglo topos dunno plateaux kapok tarot turbot deathblow foreknow overgrow regrow gateau matzoh gateaux pekoe tallyho studio buffalo patio portico stereo dynamo tableau vertigo aliquot apropos cameo domino outgrow presidio spatio tableaux adagio piccolo bandeau embryo portfolio undergo indigo bungalow calico politico medico mistletoe afterglow oregano braggadocio pistachio undertow pompano mustachio microdot moustachio impresario pianissimo archipelago generalissimo