Less than a foot (4)
I believe the answer is:
heel
'a foot' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for heel that I've seen before include "Lean over; part of foot" , "swine" , "Reprehensible person" , "tip" , "Despicable type" .)