Animal, mostly solitary, primarily inhabiting a region of Spain (9)
I believe the answer is:
catalonia
'region of spain' is the definition.
(I've seen this before)
'animal mostly solitary primarily inhabiting a' is the wordplay.
'animal' becomes 'cat' (I've seen this before**).
'mostly' means to remove the last letter.
'solitary' becomes 'alone' ('alone' can be a synonym of 'solitary').
'primarily' suggests taking the first letters.
The first letter of 'inhabiting' is 'i'.
'alone' with its final letter removed is 'alon'.
'cat'+'alon'+'i'+'a'='CATALONIA'
(Other definitions for catalonia that I've seen before include "autonomous region" , "part of Spain" , "secessionist area" , "NE region of Spain" .)