Area coldest, close against part of leg (8,6)

I believe the answer is:
achilles tendon
'part of leg' is the definition.
(I've seen this before)
'area coldest close against' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'coldest' becomes 'chillest' (I can't explain this - if you can you should believe this answer much more).
'close' becomes 'end' (close can mean to end or finish).
'against' becomes 'on' (on can mean by or up against).
'a'+'chillest'+'end'+'on'='ACHILLES' TENDON'
Can you help me to learn more?
(Other definitions for achilles tendon that I've seen before include "part of leg" , "accident spot" , "Tissue" , "sinew" , "part of body" .)
