Spaniard or Portuguese rotting in a bier (7)
I believe the answer is:
iberian
'spaniard or portuguese' is the definition.
(I know that Spaniard is a type of Iberian)
'rotting in a bier' is the wordplay.
'rotting' indicates an anagram.
'in'+'a'+'bier'='inabier'
'inabier' anagrammed gives 'IBERIAN'.
(Other definitions for iberian that I've seen before include "one from Spain, perhaps" , "from Malaga?" , "Spanish and/or Portuguese" , "south of the Pyrenees" , "Spaniard, perhaps" .)