His work should make the outlook clearer (6,7)
I believe the answer is:
window cleaner
'his work should make' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'outlook clearer' is the wordplay.
'outlook' becomes 'window' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'clearer' becomes 'cleaner' ('clean' can be a synonym of 'clear').
'window'+'cleaner'='WINDOW CLEANER'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for window cleaner that I've seen before include "One washing glass" , "He works on glass" , "Person using bucket of water? - Welder? Now I can! (anag)" .)