Virginia mounted diploma in flat (5)
I believe the answer is:
vapid
'flat' is the definition.
(I know that flat can be written as vapid)
'virginia mounted diploma' is the wordplay.
'virginia' becomes 'va' (US state abbreviation).
'mounted' says the letters should be written in reverse.
'diploma' becomes 'dip' (I can't explain this - if you can you should give a lot more credence to this answer).
'dip' written backwards gives 'pid'.
'va'+'pid'='VAPID'
'in' is the link.
Can you help me to learn more?
(Other definitions for vapid that I've seen before include "Boring, flat" , "Boring or lifeless" , "Dull, insipid, flat" , "Offering no stimulation" , "Dull and tasteless" .)