Further, nearly a foot back (3)
I believe the answer is:
too
'further' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for too that I've seen before include "As well; in addition" , "To a greater than desirable extent" , "Furthermore" , "As well, also" , "Additionally" .)