Wed posh idiot with energy (5)
I believe the answer is:
unite
'wed' is the definition.
(I've seen this in another clue)
'posh idiot with energy' is the wordplay.
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'idiot' becomes 'nit' (nit can mean a stupid person).
'with' says to put letters next to each other.
'energy' becomes 'e' (physics symbol as in E=mc2).
'u'+'nit'+'e'='UNITE'
(Other definitions for unite that I've seen before include "Link" , "old coin" , "Bring together, become one" , "Become an integrated whole" , "Amalgamate" .)