Isotonic rhymes with:
catatonic, diatonic, neoplatonic, platonic, catatonic, diatonic, hypertonic, leptonic, miltonic, neoplatonic, planktonic, platonic, plutonic, tectonic, tonic
catatonic, diatonic, neoplatonic, platonic, catatonic, diatonic, hypertonic, leptonic, miltonic, neoplatonic, planktonic, platonic, plutonic, tectonic, tonic