Plain secretaries a politician’s laid into (6)
I believe the answer is:
pampas
'plain' is the definition.
(I've seen this before)
'secretaries a politician's laid into' is the wordplay.
'secretaries' becomes 'PAs' (personal assistants).
'politician' becomes 'MP' (Member of Parliament).
'laid into' indicates putting letters inside.
'a'+'mp'='amp'
'pas' placed around 'amp' is 'PAMPAS'.
(Other definitions for pampas that I've seen before include "Vast plains of South America" , "7" , "Plains with grass" , "Grassy plains of Argentine" , "South American plain" .)