Brilliant old Peruvian lineage (12)
I believe the answer is:
incandescent
'brilliant' is the definition.
(thesaurus)
'old peruvian lineage' is the wordplay.
'old peruvian' becomes 'incan' (I've seen this before).
'lineage' becomes 'descent' ('descent' can be a synonym of 'lineage').
'incan'+'descent'='INCANDESCENT'
(Other definitions for incandescent that I've seen before include "Dazzling" , "Glowing brightly" , "Furious" , "White-hot" , "Glowing hot" .)