Base purpose (4)
I believe the answer is:
mean
I believe this is a double definition.
'base' is the first definition.
('mean' can be a synonym of 'base')
'purpose' is the second definition.
(I've seen this before)
(Other definitions for mean that I've seen before include "Despicable" , "Represent - average" , "Intend; not generous" , "Bad-tempered" , "Being near" .)