Grate cheese rind initially into mushy peas (6)
I believe the answer is:
scrape
'grate' is the definition.
(synonyms)
'cheese rind initially into mushy peas' is the wordplay.
'initially' says to take the initial letters.
'into' is an insertion indicator.
'mushy' indicates anagramming the letters (letters mushed up).
The first letters of 'cheese rind' is 'cr'.
'peas' is an anagram of 'sape'.
'cr' put into 'sape' is 'SCRAPE'.
(Other definitions for scrape that I've seen before include "Awkward situation caused by capers" , "stroke of a violin" , "Recaps about abrasion" , "Thinly-spread butter" , "Abrade in capers" .)