Quick learner (6)
I believe the answer is:
sponge
'quick learner' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for sponge that I've seen before include "Cadge; type of cake" , "Porous mass for wiping up" , "Sea animal often found in bathroom" , "that lives in the sea" , "Sea creature - cleanser - cake" .)