/ˌʌnˌkɑːnstəˈtuːʃənl̟/ /ˌʌnˌkɒnstəˈtjuːʃənl̟/. adjective. Learner's definition of UNCONSTITUTIONAL. : not allowed by the constitution of a country or government: not constitutional.ˌʌnˌkɑːnstəˈtuːʃənl̟/ /ˌʌnˌkɒnstəˈtjuːʃənl̟/. adjective. Learner's definition of UNCONSTITUTIONAL. : not allowed by the constitution of a country or government: not constitutional.