a fortiori
Concise Oxford English Dictionary © 2008 Oxford University Press:
a fortiori /ˌeɪ fɔːtɪˈɔːrʌɪ, ˌɑː, -riː/
▶adverb & adjective with a yet stronger reason than a conclusion previously accepted.
– origin C17: L., from a fortiori argumento ‘from stronger argument’.
'a fortiori' also found in these Oxford entries:

