That "one year wonder" failed at the outset (6)
I believe the answer is:
yonder
'that' is the definition.
(archaic word meaning 'that')
'one year wonder failed at the outset' is the wordplay.
I cannot quite understand how this works, but
'year' could be 'y' and 'y' is found in the answer.
'at' could be 'on' (location) and 'on' is found within the answer.
The remaining letters 'der' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for yonder that I've seen before include "Over there, somewhat archaic" , "In that direction" , "Over there, of old." , "Over there, a long time ago" , "Rodney (anag.)" .)