Spot fox coming back
I believe the answer is:
dot
'spot' is the definition.
(I've seen this before)
'fox coming back' is the wordplay.
'fox' becomes 'tod' (historic term).
'coming back' is a reversal indicator.
'tod' backwards is 'DOT'.
(Other definitions for dot that I've seen before include "Marriage portion; spot" , "Long-ago year?" , "Full stop, point" , "'Spot, tiny mark (3)'" , "scatter" .)