Thought model short (4)
I believe the answer is:
idea
'thought' is the definition.
('idea' can be a synonym of 'thought')
'model short' is the wordplay.
'model' becomes 'ideal' (ideal is a kind of model).
'short' means to remove the last letter.
'ideal' with its last letter removed is 'IDEA'.
(Other definitions for idea that I've seen before include "Notion, image" , "Proposal" , "intellectual product" , "Thought, conception" , "Aim" .)