On the retiring editor, bestows a beam of pleasure (7)
I believe the answer is:
delight
'pleasure' is the definition.
(delight is a kind of pleasure)
'on the retiring editor bestows a beam' is the wordplay.
'on' means one lot of letters go next to another.
'the retiring' shows that the letters should be reversed in order.
'editor' becomes 'ed' (abbreviation).
'bestows a beam' becomes 'light' (I can't justify this - if you can you should give a lot more credence to this answer).
'ed' backwards is 'de'.
'de'+'light' is 'DELIGHT'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for delight that I've seen before include "Give great pleasure to" , "Jubilation" , "Pleasure (possibly Turkish?)" , "It could be Turkish" , "Glee; its spirit rare, Shelley" .)