means A genus of common molds, recognizable by their brush-shaped spore-bearing structures, some species of which produce penicillin and others ripen cheeses.

from From Latin 'penicillus,' meaning 'little brush' or 'painter's brush' — itself a diminutive of 'penis,' which to the Romans simply meant 'tail.' Botanists peering through microscopes saw the mold's spore-bearing tips fanning out like the bristles of a tiny brush and named it accordingly. The same root gives us 'pencil,' which began life as a fine artist's brush before it ever held graphite.