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