Of a fever: recurring every eighth day (by inclusive reckoning every ninth day).
Origin
Early 17th century (in an earlier sense). From classical Latin nōnus ninth + -an, probably after French †nonane. Compare classical Latin nōnānus belonging to the ninth legion.
Definition of nonan in US English:
nonan
adjectiveˈnəʊnən
Medicine rare, historical
Of a fever: recurring every eighth day (by inclusive reckoning every ninth day).
Origin
Early 17th century (in an earlier sense). From classical Latin nōnus ninth + -an, probably after French † nonane. Compare classical Latin nōnānus belonging to the ninth legion.