Coparcenary Definition: An obsolete co-ownership mechanism of English law where property, if there was no will, always went to the eldest son. An obsolete co-ownership mechanism of English law where property, if there was no will, always went to the eldest son. If there was no male heir, the property went to all the female children collectively in co-ownership. Find you are constantly looking up definitions? Try our search provider (works in most modern browsers) If you find an error or omission in Duhaime's Legal Dictionary, or if you have legal term suggestion, we'd love to hear from you!