Sits uncomfortably after core text survives (6)
I believe the answer is:
exists
'survives' is the definition.
('exist' can be a synonym of 'survive')
'sits uncomfortably after core text' is the wordplay.
'uncomfortably' indicates anagramming the letters.
'after' says to put letters next to each other.
'core text' becomes 'ex' (I can't justify this - if you can you should believe this answer much more).
'sits' is an anagram of 'ists'.
'ists' after 'ex' is 'EXISTS'.
Can you help me to learn more?
(Other definitions for exists that I've seen before include "Subsists" , "Is extant" , "Has life" , "Lives" , "Is present in the universe" .)