Well-known in association with a medium (5)
I believe the answer is:
famed
'well-known' is the definition.
(I know that well-known can be written as famed)
'association with a medium' is the wordplay.
'association' becomes 'fed' (I can't justify this - if you can you should give a lot more credence to this answer).
'with' is an insertion indicator.
'medium' becomes 'm' (as in UK clothing sizes).
'a'+'m'='am'
'fed' enclosing 'am' is 'FAMED'.
'in' is the link.
Can you help me to learn more?
(Other definitions for famed that I've seen before include "Renowned" , "Well-known" , "Noted" , "Eminent" , "Acclaimed" .)