Decidedly rhymes with:
splendidly, acidly, advisedly, allegedly, assuredly, avidly, avowedly, belatedly, blessedly, contentedly, deservedly, determinedly, doggedly, excitedly, intrepidly, markedly, morbidly, rapidly, reportedly, ruggedly, solidly, splendidly, stupidly, supposedly, timidly, unashamedly, vividly
Decidedly sounds like:
dactyl, desautel, deshotel, diastole, digital, digitally, distal, distel, distil, distill, doggedly, dostal, ductile, dugdale