Abuse popular American returning to Lithuania (6)
I believe the answer is:
insult
'abuse' is the definition.
('insult' can be a synonym of 'abuse')
'popular american returning to lithuania' is the wordplay.
'popular' becomes 'in'.
'american' becomes 'us'.
'returning' shows that the letters should be reversed in order.
'to lithuania' becomes 'lt' (internet domain code for Lithuania).
'us' in reverse letter order is 'su'.
'in'+'su'+'lt'='INSULT'
(Other definitions for insult that I've seen before include "Speak or act inm abusive way" , "Treat with contempt" , "Slander" , "An addition to injury?" , "Demeaning remark" .)