I suddenly felt unutterably depressed.
我突然感到莫名的惆怅。
柯林斯例句
These two felt unutterably bound to each other.
这两个人都觉得极其难舍难分.
辞典例句
"she was looking very young tonight, and, as usual, indescribably beautiful, in a simple strapless dress of a green and white silky cotton"