unthinkable /ʌnˈθɪŋkəbəl/adjective 3noun 1forms 3 adjective3 •That cannot be believed. •Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.Nothing is unthinkable, nothing impossible to the balanced person, provided it comes out of the needs of life and is dedicated to life's further development •Extremely improper; extremely at odds with norms of expected behavior. noun1 •Something, or various things collectively, that one dares not think about or do.do the unthinkabledid the unthinkable formsunthinkables · more unthinkable · most unthinkable