Achilles is one poorly noted name (6)
I believe the answer is:
tendon
'achilles' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'one poorly noted name' is the wordplay.
'one poorly' is an anagram indicator (a poor spelling).
'name' becomes 'n' (common abbreviation e.g. on forms).
'noted' with letters rearranged gives 'tendo'.
'tendo'+'n'='TENDON'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for tendon that I've seen before include "personal connecting link" , "Ligament - sinew" , "Strong cord of tissue connecting muscle" , "Strong tissue that connects muscle" , "It's attaches tissue to bone" .)