Outline is almost exact (6)
I believe the answer is:
precis
'outline' is the definition.
(synonyms)
'almost exact' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'exact' becomes 'precise' (associated in meaning).
'precise' with its final letter taken away is 'PRECIS'.
'is' acts as a link.
(Other definitions for precis that I've seen before include "Prices for abbreviated version" , "Summarize" , "Synopsis, summary" , "Summary of the main points" , "Summary, short version" .)