Nightmare with stomach after virus? (7)
I believe the answer is:
bugbear
'nightmare' is the definition.
(thesaurus)
'stomach after virus?' is the wordplay.
'stomach' becomes 'bear' (both can mean to tolerate or endure).
'after' means one lot of letters go next to another.
'virus?' becomes 'bug'.
'bear' after 'bug' is 'BUGBEAR'.
'with' acts as a link.
(Other definitions for bugbear that I've seen before include "Obsessive idea" , "Cause of excessive anxiety" , "Nasty goblin - cause of fear" , "pet hate" , "Cause of irritation" .)