Temperate media executive became serious (7)
I believe the answer is:
sobered
'became serious' is the definition.
(I've seen this before)
'temperate media executive' is the wordplay.
'temperate' becomes 'sober' (I've seen this in another clue).
'media executive' becomes 'ed' (I can't explain this - if you can you should give a lot more credence to this answer).
'sober'+'ed'='SOBERED'
Can you help me to learn more?
(Other definitions for sobered that I've seen before include "no longer excited" , "Became serious" , "calmed down" , "On the wagon" .)