Erudite academic, old, and German (8)
I believe the answer is:
profound
'erudite' is the definition.
(thesaurus)
'academic old and german' is the wordplay.
'academic' becomes 'prof' (short for professor).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'and german' becomes 'und' ('and' in German).
'prof'+'o'+'und'='PROFOUND'
(Other definitions for profound that I've seen before include "unqualified" , "Extensive" , "Showing great insight" , "Far-reaching" , "Deep; intense" .)