indescribable

Word family (noun) description (adjective) describableindescribable nondescript descriptive (verb) describe (adverb) descriptively
From Longman Dictionary of Contemporary Englishindescribablein‧de‧scri‧ba‧ble /ˌɪndɪˈskraɪbəbəl◂/ adjective    EXPRESSsomething that is indescribable is so terrible, so good, so strange etc that you cannot describe it, or it is too difficult to describe  a feeling of indescribable joyindescribably adverb  an indescribably awful smellExamples from the CorpusindescribableThe chaos and confusion was indescribable.But the experience itself is essentially non-rational and indescribable.Unlimited discomfort would of course be indescribable.The sky, that had been so grey and lowering, was iridescent with indescribable beauty.Fresh salmon has an indescribable flavor.I woke up on the day after my wedding with a feeling of indescribable joy.There is a space around it, an indescribable presence.Then I skipped down the entry ladder with indescribable relief.There is an indescribable sense of community here.