Compels us to appear in a complicated case (6)
I believe the answer is:
causes
'compels' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their -s form.
Maybe you can see a link between them that I don't see?
'us to appear in a complicated case' is the wordplay.
'to appear in' is an insertion indicator.
'a complicated' is an anagram indicator (a complex or confusing ordering of the letters).
'case' with letters rearranged gives 'caes'.
'us' placed within 'caes' is 'CAUSES'.
Can you help me to learn more?
(Other definitions for causes that I've seen before include "Factors" , "Reasons why things happen" , "'Reasons, grounds (6)'" , "They produce effects" , "Origins or crusaders" .)