By autumn, Fawkes was one? (4,3)
I believe the answer is:
fall guy
'one?' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'by autumn fawkes' is the wordplay.
'by' means one lot of letters go next to another.
'autumn' becomes 'fall' (synonyms).
'fawkes' becomes 'guy' (gunpowder plotter Guy Fawkes).
'fall' put next to 'guy' is 'FALL-GUY'.
'was' is the link.
(Other definitions for fall guy that I've seen before include "Patsy" , "Aunt Sally" , "who's not 18 [UPRIGHT]?" , "Scapegoat" , "Dupe" .)