Anything conjoined consists of more than one entity. Conjoined twins are physically connected.
About 200 years ago, two individuals known to the West as Chang and Eng were born in Siam (modern-day Thailand) conjoined (connected) at the sternum. Their fame gave rise to the now disused term Siamese twins, which has been replaced by conjoined twins. The somewhat infrequent verb conjoin — which provides the inspiration for the adjective conjoined — means to come together with a common purpose. You could say two people who share the same beliefs have conjoined minds.