the ineffable sadness of many of the portraits许多肖像流露出的难以形容的悲伤

the mystical notion of an ineffable God不得直呼上帝名讳的神秘观念

There is an extra, ineffable quality to his voice that makes it awfully easy on the ear.他的声音别有一种难以形容的特质, 极其悦耳动听。