For the not very intelligent, it's easy (6)
I believe the answer is:
simple
'easy' is the definition.
(associated in meaning)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for simple that I've seen before include "Easily done/understood" , "Plant with medicinal properties" , "Easy to understand" , "Easily done" , "Elementary" .)