Entry 1 sense Webster, 1913 Unreasonable /ən-rēz'-nəb-əl/ · Un·rea·son·a·ble · IPA /ʌnˈɹiːz.(ə)nə.bl̩/ 01 a. Not reasonable; irrational; immoderate; exorbitant. 1. Not reasonable; irrational; immoderate; exorbitant.