Fixation over air in Lisbon (4)
I believe the answer is:
fado
'air in lisbon' is the definition.
The definition suggests a singular noun which matches the answer.
'fixation over' is the wordplay.
'fixation' becomes 'fad' (I can't justify this - if you can you should give a lot more credence to this answer).
'over' becomes 'o' (cricket abbreviation).
'fad'+'o'='FADO'
Can you help me to learn more?
(Other definitions for fado that I've seen before include "Portuguese traditional dance and doleful song" , "Portuguese folk song" , "Melancholy style of song popular in Portugal" , "Popular Portuguese song, often melancholy" , "Portuguese song genre" .)