The word "querulous" which we use in English is taken from the Old French language used in the late 15th Century (1450 A.D.). They used querelos which means "quarrelsome, argumentative". The french took it from the Late Latin (the one used in the Western Roman Empire) querulosus . Querulosos was taken from Latin querulus,"full of complaints, complaining". Querelus is derivated from queri which means "to complain".
Latin - Latin - Late Latin - Old French - English