Lean part of the foot (4)
I believe the answer is:
heel
I believe this is a double definition.
'lean' is the first definition.
(thesaurus)
'part of the foot' is the second definition.
(I've seen this before)
(Other definitions for heel that I've seen before include "knob" , "Achilles's weak spot" , "tip" , "Part of shoe; bad person" , "3's weak point" .)