Theoretical rhymes with:
heretical, alphabetical, antithetical, heretical, parenthetical, acoustical, alphabetical, analytical, antithetical, apolitical, astronautical, biopharmaceutical, critical, dialectical, ecclesiastical, egotistical, elliptical, fanatical, floptical, geopolitical, heretical, hypercritical, hypocritical, identical, logistical, mathematical, mystical, nonpolitical, optical, parenthetical, pharmaceutical, problematical, sabbatical, statistical, tactical, testicle, uncritical, vertical, viatical
Theoretical sounds like:
tartaglia, theoretically, threadgill