An attempt to indicate time past (3)
I believe the answer is:
ago
'time past' is the definition.
(I've seen this in another clue)
'an attempt to indicate' is the wordplay.
I cannot quite see how this works, but
'an' could be 'a' and 'a' is found in the answer.
'attempt' could be 'go' (go is a kind of attempt) and 'go' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ago that I've seen before include "Previously" , "Gone, past, since" , "Time past" , "Back (in time)" , "Earlier, gone by" .)