Crossword Genius

Proud US rival I go on about (12)

Ross

I believe the answer is:

vainglorious

'proud' is the definition.
('vainglorious' can be similar in meaning to 'proud')

'us rival i go on about' is the wordplay.
'about' indicates an anagram.
'us'+'rival'+'i'+'go'+'on'='usrivaligoon'
'usrivaligoon' anagrammed gives 'VAINGLORIOUS'.

(Other definitions for vainglorious that I've seen before include "Cocky" , "Self-important -- savouring oil (anag)" , "Boasting" , "Boastful; rousing viola (anag.)" , "Excessively self-important" .)

I've seen this clue in The Telegraph.
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