Thesaurus

1000th, 100th, 101st, 105th, 10th, 110th, 115th, 11th, 120th, 125th, 12th, 130th, 135th, 13th, 140th, 145th, 14th, 150th, 155th, 15th, 160th, 165th, 16th, 170th, 175th, 17th, 180th, 18th, 190th, 19th, 1st, 200th, 20th, 21st, 22nd, 23rd, 24th, 25th, 26th, 27th, 28th, 29th, 2d, 2nd, 300th, 30th, 31st, 32nd, 33rd, 34th, 35th, 36th, 37th, 38th, 39th, 3rd, 400th, 40th, 41st, 42nd, 43rd, 44th, 45th, 46th, 47th, 48th, 49th, 4th, 500th, 50th, 55th, 5th, 60th, 64th, 65th, 6th, 70th, 75th, 7th, 80th, 85th, 8th, 90th, 95th, 9th, billionth, centesimal, eighteenth, eighth, eightieth, eighty-fifth, eleventh, fifteenth, fifth, fiftieth, fifty-fifth, first, five-hundredth, fortieth, forty-eighth, forty-fifth, forty-first, forty-fourth, forty-ninth, forty-second, forty-seventh, forty-sixth, forty-third, four-hundredth, fourteenth, fourth, hundred-and-eightieth, hundred-and-fifteenth, hundred-and-fifth, hundred-and-fiftieth, hundred-and-fifty-fifth, hundred-and-first, hundred-and-fortieth, hundred-and-forty-fifth, hundred-and-ninetieth, hundred-and-seventieth, hundred-and-seventy-fifth, hundred-and-sixtieth, hundred-and-sixty-fifth, hundred-and-tenth, hundred-and-thirtieth, hundred-and-thirty-fifth, hundred-and-twentieth, hundred-and-twenty-fifth, hundredth, millionth, n-th, nineteenth, ninetieth, ninety-fifth, ninth, nth, ordinal, quadrillionth, quaternary, quintillionth, second, seventeenth, seventh, seventieth, seventy-fifth, sixteenth, sixth, sixtieth, sixty-fifth, sixty-fourth, tenth, tertiary, third, thirteenth, thirtieth, thirty-eighth, thirty-fifth, thirty-first, thirty-fourth, thirty-ninth, thirty-second, thirty-seventh, thirty-sixth, thirty-third, thousandth, three-hundredth, trillionth, twelfth, twentieth, twenty-eighth, twenty-fifth, twenty-first, twenty-fourth, twenty-ninth, twenty-second, twenty-seventh, twenty-sixth, twenty-third, two-hundredth, umpteenth, umptieth, umteenth, zero, zeroth

21st is a ADJ.