Undependable (adjective)

1. Not able to be relied on; not dependable.
2. Not trustworthy or reliable.

Origin:

Late 19th century: from un-1 + dependable, on the pattern of words such as unreliable.

Examples:

1. The car is undependable and always breaking down.
2. The employee was fired for being undependable and often absent from work.
3. The weather forecast is undependable, so it's best to be prepared for any eventuality.
4. The undependable witness could not be relied on to give accurate testimony.
5. The undependable system failed during the crucial moment.