Part of foot (4)
(Other definitions for heel that I've seen before include "afoot?" , "tip" , "Rotten type" , "horrible person" , "Back of 15 across" .)
'part of foot' is the definition.
(12 inches in a foot)
This is the entire clue.
(Other definitions for inch that I've seen before include "0.0254 metre" , "Scottish island: unit of length" , "Subdivision of 14 down" , "One 63,360th of a mile" , "Short measure; island" .)
(Other definitions for ankle that I've seen before include "Bone over foot" , "Narrow part of leg" , "Leg-joint" , "Human joint" , "Part of the leg between the foot and the shin" .)