|ən|fāliŋ, -lēŋ adjective
Etymology: Middle English, from un- (I) + failing, present participle of failen to fail
: not failing or liable to fail:
a. : not desisting : constant , unflagging
unfailing good spirits
unfailing courtesy
b. : everlasting , inexhaustible
a subject of unfailing interest
unfailing pleasure
c. : infallible , sure
an unfailing test
the unfailing mark of an amateur