Thought I'd half of each (4)
I believe the answer is:
idea
'thought' is the definition.
(I know that thought can be written as idea)
'i'd half of each' is the wordplay.
'half of' suggests halving the letters.
'each' halved is 'ea'.
'id'+'ea'='IDEA'
(Other definitions for idea that I've seen before include "Notion in the mind" , "Content of cognition" , "Proposal" , "Plan" , "Product of the mind" .)