1) Always able to supply more 2) Foolproof 3) Inexhaustible 4) Infallible 5) Not failing 6) Not giving way 7) Not liable to failure 8) Unceasing 9) Unfailing good humor Found on https://www.crosswordclues.com/clue/unfailing
not failing; not giving way; not falling short of expectation; completely dependable: an unfailing friend. · inexhaustible; endless: unfailing resources; unfailing good humor. Found on https://www.infoplease.com/dictionary/unfailing