Mean not to go in the water (6)
I believe the answer is:
denote
'mean' is the definition.
(denoting is a kind of meaning)
'not to go in the water' is the wordplay.
'to go in' means one lot of letters goes inside another.
'the water' becomes 'dee' (I am not sure about this - if you are sure you should believe this answer much more).
'not' inserted inside 'dee' is 'DENOTE'.
Can you help me to learn more?
(Other definitions for denote that I've seen before include "Point" , "Be an indication of" , "Mean or signify" , "Be the sign or symbol of" , "Designate" .)