Cleistothecium is a botanical term referring to a structure produced by certain fungi that contains their reproductive cells. Although not commonly used in everyday language, there are some synonyms that can be used to describe this structure. These include ascocarp, which is a more general term for the spore-bearing structure produced by certain fungi, and perithecium, which is a similar structure produced by different fungal groups. Another synonym that can be used is sporocarp, which is a term used to describe any structure that contains spores or gametes, and is therefore applicable to structures produced by various types of organisms, including fungi.