Mentioned one dip by mistake (6)
I believe the answer is:
opined
'mentioned' is the definition.
'one dip by mistake' is the wordplay.
'by mistake' indicates anagramming the letters.
'one'+'dip'='onedip'
'onedip' with letters rearranged gives 'OPINED'.
(Other definitions for opined that I've seen before include "Conjectured" , "Supposed" , "Gave as view or thought" , "Gave as one's view" , "Expressed as one's view" .)