Behold doctor under a little pressure showing poise (6)
I believe the answer is:
aplomb
'poise' is the definition.
('aplomb' can be a synonym of 'poise')
'behold doctor under a little pressure' is the wordplay.
'behold' becomes 'lo'.
'doctor' becomes 'mb' (Bachelor of Medicine, Medicinae Baccalaureus**).
'under' says to put letters next to each other.
'little' suggests taking the first letters.
The initial letter of 'pressure' is 'p'.
'lo'+'mb'='lomb'
'a'+'p'='ap'
'lomb' put after 'ap' is 'APLOMB'.
'showing' acts as a link.
(Other definitions for aplomb that I've seen before include "coolness is required" , "Self-satisfied dignity, complacency" , "Nonchalant confidence" , "Self-satisfied dignity and confidence" , "Cool self-assurance" .)