Wiktionary
cyclopentanepentone
n. (context organic compound English) A cyclic oxocarbon derived from cyclopentane
Wikipedia
Cyclopentanepentone
Cyclopentanepentone, also known as leuconic acid, is a hypothetical organic compound with formula CO, the fivefold ketone of cyclopentane. It would be an oxide of carbon (an oxocarbon), indeed a pentamer of carbon monoxide.
As of 2000, the compound had yet to be synthesized in bulk, but there have been reports of trace synthesis.