It's bound to mean a change of plea (4)
I believe the answer is:
leap
'it's bound' is the definition.
(synonyms)
'mean a change of plea' is the wordplay.
'plea' can be anagrammed to 'LEAP'.
Though, I am unsure how the anagram is indicated.
'to' is the link.
Can you help me to learn more?
(Other definitions for leap that I've seen before include "Sudden bound" , "identify extra day?" , "Jump suddenly" , "Sort of year" , "Jump across" .)