Unreliable (adjective)

1. Not able to be trusted or relied upon.
2. Inconsistent or undependable.

Origin:

Late 19th century: from un-1 (expressing negation) + reliable.

Examples:

1. The car was deemed unreliable due to its frequent breakdowns.
2. The witness was considered unreliable due to inconsistencies in their testimony.
3. His promises were unreliable and often not kept.
4. The source of information was unreliable and therefore not used.
5. The network was deemed unreliable due to frequent outages.