unfailing

Always able to supply more; inexhaustible.

Constant; unflagging.

Incapable of error; infallible.

Not liable to fail; incapable of being exhausted: as, an unfailing spring; unfailing sources of supply.

Not missing; always fulfilling a hope, promise, or want; not coming short; sure; certain.

Not failing; not liable to fail; inexhaustible; certain; sure.

inexhaustible

changeless

infallible

not liable to failure