Horse around a lot in the middle of Oslo (8)
I believe the answer is:
stallion
'horse' is the definition.
(thesaurus)
'around a lot in the middle of oslo' is the wordplay.
'around' indicates anagramming the letters.
'the middle of' means to look at the middle letters.
The centre of 'oslo' is 'sl'.
'a'+'lot'+'in'+'sl'='alotinsl'
'alotinsl' with letters rearranged gives 'STALLION'.
(Other definitions for stallion that I've seen before include "Male horse, often used for breeding" , "Male steed" , "Uncastrated adult male horse" , "Male horse kept for breeding" , "Male horse lost in atolls" .)