Constant speed of bandit at sea? (6)
I believe the answer is:
pirate
'bandit at sea?' is the definition.
'constant speed' is the wordplay.
'constant' becomes 'pi' (mathematics: 3.14).
'speed' becomes 'rate' (the speed at which something happens).
'pi'+'rate'='PIRATE'
'of' is the link.
(Other definitions for pirate that I've seen before include "One who infringes another's copyright" , "Copyright infringer" , "Robber on the high scas" , "Use (another's work) for profit without permission" , "Teach, perhaps" .)