A doctor with oxygen — it is nifty (6)
I believe the answer is:
adroit
'nifty' is the definition.
Both the definition and answer are adjectives. Maybe you can see an association between them that I can't see?
'a doctor with oxygen it' is the wordplay.
'doctor' becomes 'Dr' (abbreviation).
'with' means one lot of letters go next to another.
'oxygen' becomes 'O' (atomic symbol for oxygen).
'a'+'dr'+'o'+'it'='ADROIT'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for adroit that I've seen before include "Quick and deft" , "Skilled" , "resourceful" , "Clever - crafty" , "Quick and clever in action or thought" .)