Underpass rhymes with:
overpass, boardingpass, bumpass, bypass, overpass, trespass, worldpass, airgas, amerigas, bluegrass, boardingpass, bumpass, bypass, eelgrass, energas, eyeglass, fiberglas, fiberglass, hourglass, jackass, landmass, outclass, overpass, piepgras, plexiglas, plexiglass, sassafras, serfass, shortgrass, snodgrass, spyglass, sunglass, tallgrass, trespass, underclass, upperclass, worldpass, yankass