Plain action of speaker (6)
I believe the answer is:
steppe
'plain' is the definition.
(I know that steppe is a type of plain)
'action of speaker' is the wordplay.
'action' becomes 'step' (step is a kind of action).
'of speaker' becomes 'pe' (I can't explain this - if you can you should give a lot more credence to this answer).
'step'+'pe'='STEPPE'
Can you help me to learn more?
(Other definitions for steppe that I've seen before include "Edxtensive plain" , "Treeless plain of Russia" , "Flat area of eastern Europe or Russia" , "Large area of unforested grassland" , "plain territory" .)