Said to be good, though Sep's upset about it (5)
I believe the answer is:
spoke
'said' is the definition.
The definition and answer can be both to do with communicating as well as being past participle verbs.
Maybe you can see an association between them that I don't see?
'good though sep's upset about it' is the wordplay.
'good though' becomes 'ok' (I am not sure about this - if you are sure you should believe this answer much more).
'upset' indicates an anagram.
'about it' indicates putting letters inside (some letters go around or about others).
'sep' anagrammed gives 'spe'.
'ok' going inside 'spe' is 'SPOKE'.
'to be' acts as a link.
Can you help me to learn more?
(Other definitions for spoke that I've seen before include "Said something" , "Rung" , "Radiating rod" , "Radius" , "gave address" .)