fons et origo
Concise Oxford English Dictionary © 2008 Oxford University Press:
fons et origo /ˌfɒnz ɛt ˈɒrɪgəʊ, ɒˈrʌɪgəʊ/
▶noun the source and origin of something.
– origin L., orig. as fons et origo mali ‘the source and origin of evil’.
'fons et origo' also found in these Oxford entries:

