A growing reason to remember Ayrton (5)
I believe the answer is:
senna
'a growing' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for senna that I've seen before include "given help to get in motion?" , "Natural laxative" , "Brazilian F1 champion, d. 1994" , "Champion driver.once" , "Formula One driver" .)