Not true to allegiance, duty, or vows
Lacking faith; lacking belief in something.
Unfaithful (said of people, towards their partners)
Not believing in God, religion, or a comparable ideology.
Serving to disappoint or deceive
Not observant of promises or covenants.
Suitable or fit to be relied on; worthy of dependence, reliance or trust; dependable, trustworthy
Such that either a sent packet will reach its destination, even if it requires retransmission, or the sender will be told that it didn't
Something or someone reliable or dependable