Placoid rhymes with:
altoid, bioflavonoid, colloid, conchoid, ellipsoid, fibroid, geoid, haploid, negroid, retinoid, tabloid, thyroid, typhoid
Placoid sounds like:
palest, palisade, pelchat, philistia, pillaged, placate, placed, placeta, placid, placida, placido, plagued, plaisted, plaskett, pleased, plichta, plight, ploughed, plucked, plugged, polecat, policed, polished, polycast, pool-side, poolside, populist, publicist, publicity, publicized, published