Parrot by summit (4)
I believe the answer is:
apex
'summit' is the definition.
(I've seen this in another clue)
'parrot by' is the wordplay.
'parrot' becomes 'ape' (both can mean to imitate).
'by' becomes 'x' (as in 'multiplied by').
'ape'+'x'='APEX'
(Other definitions for apex that I've seen before include "Absolute peak" , "Tip -- top" , "Culmination" , "Top, highest part" , "white collar union" .)