Detached sanatorium by a lake (8)
I believe the answer is:
clinical
'detached' is the definition.
(synonyms)
'sanatorium by a lake' is the wordplay.
'sanatorium by' becomes 'clinic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'lake' becomes 'L' (geographical abbreviation).
'clinic'+'a'+'l'='CLINICAL'
Can you help me to learn more?
(Other definitions for clinical that I've seen before include "description of a form of medicine" , "Cool and detached, or based on observed symptoms" , "Coldly efficient" , "Relating to medical treatment - detached" , "cold?" .)