Liberal – a politician first in local elections (5)
I believe the answer is:
ample
'liberal' is the definition.
(I've seen this before)
'a politician first in local elections' is the wordplay.
'politician' becomes 'mp'.
'first in' suggests taking the first letters.
The first letters of 'local elections' is 'le'.
'a'+'mp'+'le'='AMPLE'
(Other definitions for ample that I've seen before include "Plenty, more than enough" , "Plentiful; large" , "Bulky" , "Plentiful; capacious" , "Plentiful, quite enough" .)