Gaddum rhymes with:
adam, cadam, macadam, madam, madame, mcadam, adam, addendum, afrikanerdom, boredom, cadam, carborundum, chiefdom, christendom, condom, corundum, dedham, dukedom, earldom, edam, fiefdom, fordham, freedom, hildum, kingdom, leedom, macadam, madam, madame, martyrdom, mcadam, memorandum, modem, needham, nydam, odom, odum, officialdom, oldham, purdham, purdom, purdum, random, referendum, rodham, saddam, sandom, sedam, sedum, seldom, sheikdom, sodom, stardom, subkingdom, suydam, tandem, windham, windom, wisdom, wyndham
Gaddum sounds like:
gaetano, gaitan, gastineau, gaston, gastonia, gathman, gatien, gatten, gatton, gaudin, gaudino, gautney, gayden, gaytan, gayton, gedeon, gedney, geodyne, gestation, getman, gettin', gettman, gideon, gidney, gitana, gitano, goddam, goddamn, godden, godin, godina, godine, godino, godman, godown, godwin, goeden, gooden, goodenow, goodin, goodine, goodman, goodnow, goodwin, goodwine, goodwyn, gosdin, gotham, gotten, gottman, gudino, guidone, gustin, guston, gutman, gutmann, guttman, guttmann, gutwein, guyton, gyohten