unassailable adj. + Add to list US //ˌənəˈseɪɫəbəɫ// UK //ʌnɐsˈeɪləbəl// unas·sail·able SynonymsEtymology Synonyms bulletproofimpregnableinviolablesecurestrongunattackableunshakableuntouchablewatertightOrigin From un- + assailable.