nil desperandum
Concise Oxford English Dictionary © 2008 Oxford University Press:
nil desperandum /ˌdɛspəˈrandəm/
▶exclamation do not despair; never despair.
– origin from L. nil desperandum Teucro duce ‘no need to despair with Teucer as your leader’, from Horace's Odes 1.vii.27.
'nil desperandum' also found in these Oxford entries:

