Agitated American son seized by FBI agent (6)
I believe the answer is:
fussed
'agitated' is the definition.
The definition and answer can be both to do with human feelings as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?
'american son seized by fbi agent' is the wordplay.
'american' becomes 'US' (United States).
'son' becomes 's' (genealogical abbreviation for son).
'seized by' indicates putting letters inside.
'fbi agent' becomes 'fed' (short for federal agent).
'us'+'s'='uss'
'uss' placed into 'fed' is 'FUSSED'.
Can you help me to learn more?
(Other definitions for fussed that I've seen before include "Made unnecessary display about unimportant matter" , "Worried" , "Fretted" .)