The word "catadidymus" may look intimidating at first glance, but it's not as complicated as it seems. The word is spelled "kætəˈdɪdɪməs" in IPA phonetic transcription. The "cata-" prefix means "downward," and the "-didymus" suffix means "twin." Thus, "catadidymus" means having twin parts that are oriented vertically. While this may not come up in everyday conversation, knowing the spelling and meaning of obscure words like "catadidymus" can expand your vocabulary and communication skills.
A twin monster joined above but double below.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.