It's basic in maths (4)
I believe the answer is:
root
'it's basic' is the definition.
(similar in meaning)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for root that I've seen before include "Basic cause or origin" , "grub" , "Underground growth" , "Lowest part of plant" , "Derivation" .)