any member of an extinct group of marine organisms of uncertain relationships found as fossils in marine limestones of Late Precambrian and Early Cambrian age (Precambrian time ended about 542 million years ago and was followed by the Cambrian). The archaeocyathid fossils represent the calcareous supporting structure built by a creature of which little is known. Indeed, it has been considered possible that the archaeocyathid organism was some sort of calcareous algae, although this seems unlikely.
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|the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).|
|a white, crystalline, water-insoluble solid, C14H9Cl5, usually derived from chloral by reaction with chlorobenzene in the presence of fuming sulfuric acid: used as an insecticide and as a scabicide and pediculicide: agricultural use prohibited in the U.S.|