Billionth rhymes with:
millionth, millionth, millionth, corinth, eleventh, eranthe, millionth, seventh, threemonth, absinthe, amaranth, coelacanth, corinth, cynth, drenth, dushyanth, eighteenth, eleventh, eranthe, fifteenth, fourteenth, helminth, hyacinth, hyacinthe, jacinth, jacinthe, labyrinth, millionth, month, nineteenth, ninth, nth, plinth, rhodanthe, seventeenth, seventh, sixteenth, tenth, thirteenth, threemonth, umpteenth
Billionth sounds like:
balint, ballooned, beland, belinda, belland, bellante, belmont, belmonte, blamed, bland, blanda, blando, blend, blenda, blended, blind, blinded, blond, blonde, blondie, bloomed, blount, blunt, blunted, bohland, boland, bolland, bowland, boyland, bulent, byland, bylund