mala fides
Concise Oxford English Dictionary © 2008 Oxford University Press:
mala fides /ˌmeɪlə ˈfʌɪdiːz, ˌmalə ˈfiːdeɪz/ Law
▶noun bad faith; intent to deceive. ▶adjective & adverb (mala fide) in bad faith; with intent to deceive.
– origin from L.
'mala fides' also found in these Oxford entries:

