Fool I spot holding electric current (5)
I believe the answer is:
idiot
'fool' is the definition.
(synonyms)
'i spot holding electric current' is the wordplay.
'spot' becomes 'dot' (I've seen this before).
'holding' means one lot of letters goes inside another.
'electric current' becomes 'I' (physics symbol).
'dot' enclosing 'i' is 'diot'.
'i'+'diot'='IDIOT'
(Other definitions for idiot that I've seen before include "Jackass" , "Twit" , "Charlie" , "Dope" , "The - (Dostoievsky)" .)