One getting into cross-country (5)
I believe the answer is:
Here is my best explanation:
'country' is the definition.
(Spain is an example)
'one getting into cross' is the subsidiary indication.
'one' becomes 'i' (roman numeral).
'getting into' means one lot of letters goes inside another.
'cross' becomes 'span' ('span' can be a synonym of 'cross'**).
'i' going within 'span' is 'spain'.
(Other definitions for spain that I've seen before include "Iberian country", "Country bordering Andorra", "holiday destination?", "Kingdom", "Catholic country", "European monarchy", "It pains badly when in the country", "ditto", "It pains one to be out in this country" and "EU country".)