Buccaneer not showing very good speed (4)
I believe the answer is:
rate
'speed' is the definition.
(the speed at which something happens)
'buccaneer not showing very good' is the wordplay.
'buccaneer' becomes 'pirate' (synonyms).
'not showing' indicates named letters should be taken away.
'very good' becomes 'pi' (I've seen this in other clues).
'pirate' with 'pi' taken out is 'RATE'.
(Other definitions for rate that I've seen before include "Regard" , "See 11" , "Rank; fee" , "Estimate or deserve" , "Price - class - speed" .)