unfailing

adjectives

not liable to failure
"a foolproof identification system"; "the unfailing sign of an amateur"; "an unfailing test"
always able to supply more
"an unfailing source of good stories"; "a subject of unfailing interest"
is similar to
incapable of being entirely consumed or used up
"an inexhaustible supply of coal"
unceasing
"unfailing loyalty"; "unfailing good spirits"; "unflagging courtesy"