Definition of: penicillium

(pen′ə·sil′ē·əm) noun plural ·li·a (-ē·ə)
Any member of a genus (Penicillium) of ascomycetous fungi characterized by feltlike masses of tubular hyphae, and growing on decaying fruits, ripening cheese, etc. P. notatum is the principal source of penicillin. [<NL <L penicillus a pencil; so called because of resemblance of its tufts to small paint brushes]