Caeruleus

Caeruleus is a Latin adjective meaning blue or blue-gray, used in literature and taxonomy to describe blue coloration.

In biological nomenclature, caeruleus (masculine), caerulea (feminine), and caeruleum (neuter) form standard adjectival endings that may appear as a species epithet in the binomial name of many plants, animals, and fungi to indicate blue coloration.

Because of its broad use, caeruleus appears in descriptions across diverse taxa, from birds and insects to flowering plants. It does not designate a single taxon; rather, it is a descriptive term.

English derivatives include caerulean and caeruleous, used to describe blue hues such as the sky or the sea. The term is related to other color vocabularies in Latin-based scientific naming, and modern color standards often employ azure or blue for precision.