Brainchild of saint from East India (4)
I believe the answer is:
idea
'brainchild' is the definition.
(I've seen this in another clue)
'of saint from east india' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'from' is a deletion indicator.
'east'+'india'='eastindia'
'eastindia' with 'saint' removed is 'edia'.
'edia' is an anagram of 'IDEA'.
(Other definitions for idea that I've seen before include "Purpose" , "Proposal" , "Theory" , "Sudden inspiration?" , "Plato's Form is" .)