Lewis & Short

pēnĭcillum, i, n., and pēnĭcillus, i, m. dim. [peniculus], lit., a little tail; hence, acc. to diverse usage,

  1. I. A painter’s brush or pencil: caudam antiqui penem vocabant, ex quo est propter similitudinem penicillus, Cic. Fam. 9, 22, 2; id. Or. 22, 74; Quint. 2, 21, 24: setae e penicillis tectoriis, Plin. 28, 17, 71, § 235; Paul. Sent. 3, 6, 63.
    1. B. Transf.
      1. 1. Painting. Plin. 35, 9, 36, § 60.
      2. 2. Style of composition: modo mihi date Britanniam, quam pingam coloribus tuis, penicillo meo, Cic. Q. Fr. 2, 15, 2.
  2. II. A roll of lint, a tent, for wounds, etc., Cels. 2, 10; 7, 7, 6; Plin. 34, 11, 26, § 113.
  3. III. A small sponge, Col. 12, 18; Plin. 9, 45, 69, § 148.
  4. IV. A kind of eye-salve, Inscr. Tōchon, Cachets des Ocul. pp. 66 and 71.