Firm doctor adopts attitude that is calm and unruffled (8)
I believe the answer is:
composed
'unruffled' is the definition.
(similar in meaning)
'firm doctor adopts attitude' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'doctor' becomes 'md' (synonyms).
'adopts' is an insertion indicator.
'attitude' becomes 'pose' (attitude can mean a pose or stance).
'md' enclosing 'pose' is 'mposed'.
'co'+'mposed'='COMPOSED'
'that is calm and' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for composed that I've seen before include "What poet did" , "Calm and collected" , "as score must be" , "with aplomb" , "appear unflappable" .)