locus classicus
Concise Oxford English Dictionary © 2008 Oxford University Press:
locus classicus /ˌləʊkəs ˈklasɪkəs, ˌlɒkəs/
▶noun (pl. loci classici /ˌləʊsʌɪˈklasɪsʌɪ, ˌlɒkiː ˈklasɪkiː/) the best known or most authoritative passage on a subject.
– origin L., lit. ‘classical place’.
'locus classicus' also found in these Oxford entries:

