undependable

This old car is undependable, so I prefer to take the bus.

用法提示：undependable 作表语形容词，描述主语的特征，意为“不可靠的”。

He lost his job because he was undependable and often arrived late.

用法提示：undependable 作表语，说明人的性格，表示“靠不住的”。

The weather forecast is undependable in this region, so always carry an umbrella.

用法提示：undependable 作表语，说明事物的可信度低，意为“不可靠的”。