1990-91 World Grand Prix champion (5)
I believe the answer is:
senna
'1990-91 world grand prix champion' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for senna that I've seen before include "Tropical plant with medicinal leaflets" , "should make you want to go quickly" , "Laxative from pods" , "Natural laxative" , "He drove fast" .)