Explorer crossing river on borders of Amazonian land (7)
I believe the answer is:
andorra
'land' is the definition.
(I know that Andorra is a European country)
'explorer crossing river on borders of amazonian' is the wordplay.
'explorer' becomes 'Dora' (Dora the Explorer, children's TV character).
'crossing' means one lot of letters goes inside another.
'river' becomes 'r' (abbreviation for river).
'on' means one lot of letters go next to another.
'borders of' suggests removing the centre.
'amazonian' with its centre removed is 'an'.
'dora' placed around 'r' is 'dorra'.
'dorra' put after 'an' is 'ANDORRA'.
(Other definitions for andorra that I've seen before include "Principality between France and Spain" , "ditto" , "Land up, perhaps" , "Radar on (anag) - European principality" , "Small European country" .)