Bird with posh date arranged going round in carriage (8)
I believe the answer is:
attitude
'carriage' is the definition.
(thesaurus)
'bird with posh date arranged going round' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'with' is a charade indicator (letters next to each other).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-U).
'arranged' indicates an anagram.
'going round' is an insertion indicator (some letters go around others).
'date' anagrammed gives 'atde'.
'tit'+'u'='titu'
'titu' placed within 'atde' is 'ATTITUDE'.
'in' acts as a link.
(Other definitions for attitude that I've seen before include "Physical or mental orientation" , "Position, stance on matter" , "Frame of mind" , "Settled way of thinking" , "Haigha's showed typical Anglo-Saxon" .)