A most unfriendly conclusion regarding part of leg (8,6)
I believe the answer is:
achilles tendon
'part of leg' is the definition.
(I've seen this before)
'a most unfriendly conclusion regarding' is the wordplay.
'most unfriendly' becomes 'chillest' (I can't justify this - if you can you should give a lot more credence to this answer).
'conclusion' becomes 'end' (something's conclusion is its end).
'regarding' becomes 'on' (on or regarding a particular topic).
'a'+'chillest'+'end'+'on'='ACHILLES' TENDON'
Can you help me to learn more?
(Other definitions for achilles tendon that I've seen before include "Tissue" , "part of leg" , "part of body" , "accident spot" , "sinew" .)