not liable to failure; "a foolproof identification system"; "the unfailing sign of an amateur"; "an unfailing test"
If you describe someone's good qualities or behaviour as unfailing, you mean that they never change. He had the unfailing care and support of Erica, his wife He continued to appear in the office with unfailing regularity thereafter. + unfailingly un·fail·ing·ly He was unfailingly polite to customers Foreigners unfailingly fall in love with the place. always there, even in times of difficulty or trouble unfailing help/support etc
unceasing; "unfailing loyalty"; "unfailing good spirits"; "unflagging courtesy" always able to supply more; "an unfailing source of good stories"; "a subject of unfailing interest