emphasis You use indescribable to emphasize that a quality or condition is very intense or extreme, and therefore cannot be properly described. her indescribable joy when it was confirmed her son was alive = inexpressible + indescribably in·de·scrib·ably indescribably filthy conditions. something that is indescribable is so terrible, so good, so strange etc that you cannot describe it, or it is too difficult to describe