The outermost protective envelope or layer surrounding a bacterial spore, sitting outside the spore coat.
From Latin 'exo-' (outside) + 'spore' + '-ium' (neuter singular suffix). Specialized bacteriological term that became precise in the late 20th century with electron microscopy revealing spore ultrastructure.
The exosporium is like a protective sleeping bag for bacteria—in anthrax spores (which sadly became infamous), the exosporium contains special proteins that help the spore evade the immune system.
Complete word intelligence in one call. Free tier — 50 lookups/day.