Wasted one's time (3)
I believe the answer is:
eon
'time' is the definition.
(I know that eon is a type of geologic time)
'wasted one's' is the wordplay.
'wasted' indicates anagramming the letters.
'one' is an anagram of 'EON'.
(Other definitions for eon that I've seen before include "Vast age; eternity" , "Very long age" , "Prolonged period" , "In time, long division" , "plenty of time" .)