Poet overlooking British and our enthusiasm (6)
I believe the answer is:
ardour
'enthusiasm' is the definition.
(ardour is a kind of enthusiasm)
'poet overlooking british and our' is the wordplay.
'poet' becomes 'bard' (bard is a kind of poet).
'overlooking' indicates named letters should be taken away.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'and' says to put letters next to each other.
'bard' with 'b' taken away is 'ard'.
'ard'+'our'='ARDOUR'
(Other definitions for ardour that I've seen before include "Intense eagerness" , "Great fire" , "Intense feeling (of love?)" , "Passion and intensity" , "Fervour, zeal" .)