A quiet look by doctor showing confidence (6)
I believe the answer is:
aplomb
'confidence' is the definition.
(thesaurus)
'a quiet look by doctor' is the wordplay.
'a quiet' becomes 'ap' (I've seen this in other clues**).
'look' becomes 'lo'.
'by' says to put letters next to each other.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus).
'ap'+'lo'+'mb'='APLOMB'
'showing' is the link.
(Other definitions for aplomb that I've seen before include "Self-confidence, assurance" , "Dignified self-confidence" , "Self-possession, assurance" , "Self-satisfied poise" , "Self-satisfied dignity, complacency" .)