One reservist – learner – in unknown country (5)
I believe the answer is:
italy
'country' is the definition.
(I know that Italy is a European country)
'one reservist learner in unknown' is the wordplay.
'one' becomes 'a' (a thing is one thing).
'reservist' becomes 'it' (I am not sure about this - if you are sure you should believe this answer much more).
'learner' becomes 'l' (as in a learner driver with L-plates on their car).
'in' indicates putting letters inside.
'unknown' becomes 'y' (algebra).
'it'+'l'='itl'
'a' placed within 'itl' is 'ital'.
'ital'+'y'='ITALY'
Can you help me to learn more?
(Other definitions for italy that I've seen before include "Catholic country" , "Land of Tuscany and Umbria" , "Problematical (informal)" , "Southern European country" , "Country shaped like a boot" .)