Please cut out guess (9)
I believe the answer is:
speculate
'guess' is the definition.
(I know that guess is a kind of speculate)
'please cut out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'please'+'cut'='pleasecut'
'pleasecut' is an anagram of 'SPECULATE'.
(Other definitions for speculate that I've seen before include "Bet; theorise" , "As before, observe" , "Surmise" , "Form opinion without definite knowledge" , "Guess without knowing the facts" .)