- foolproof, unfailing - not liable to failure; "a foolproof identification system"; "the unfailing sign of an amateur"; "an unfailing test"
Antonym: fallible (indirect, via infallible)
- unfailing - always able to supply more; "an unfailing source of good stories"; "a subject of unfailing interest"
Antonym: exhaustible (indirect, via inexhaustible)
- unfailing, unflagging - unceasing; "unfailing loyalty"; "unfailing good spirits"; "unflagging courtesy"
Antonym: inconstant (indirect, via constant)