For instance,discus and dish and disk and dais all spring from Latin discus. ( See the discuss at DOublets.) The same phenomenon is observable within English itself through the operation of dialectal pronunciation. An ordinary word will have a peculiar way of being pronounced in a dialect, that pronunciation will be given a more or less descriptive spelling so it can be represented in print, and then the pronunciation spelling will become perceived as a separate word. Ornery is one of these.
Ornery begin simply as a dialectal pronunciation of ordinary. It is attested in both British and American English during the nineteenth century. Its earliest use seems to have been as substitute for Ordinary; this sense is attested here and there for about a century: