Arbitrarily rhymes with:
unnecessarily, angrily, centrally, cerebrally, coralie, customarily, eerily, extraordinarily, farrelly, florally, hungrily, kiraly, merrily, militarily, momentarily, morally, necessarily, neutrally, oralie, orally, orchestrally, ordinarily, oreilly, primarily, satisfactorily, secondarily, severally, statutorily, temporarily, unnecessarily, voluntarily, warily, wearily