pencilyoudaoicibaDictYouDict[pencil 词源字典]
pencil: [14] Etymologically, a pencil is a ‘little penis’. It originally denoted a ‘paintbrush’ – the current sense ‘writing implement filled with a graphite rod’ did not emerge until the 17th century – and came via Old French pincel from Vulgar Latin *pēnicellum, an alteration of Latin pēnicillum ‘paintbrush’. This was a diminutive form of pēniculus ‘brush’, which was in turn a diminutive of pēnis. Pēnis originally meant ‘tail’ (whence the metaphor of the ‘brush’), and only by extension was it used for ‘male sex organ’ (in which sense English adopted it as penis [17]).

The term penicillin [20] was based on Latin pēnicillum, in allusion to the tuft-like shape of its spore-bearing structures.
=> penicillin, penis[pencil etymology, pencil origin, 英语词源]
pencil (n.)youdaoicibaDictYouDict
early 14c., "an artist's fine brush of camel hair," from Old French pincel "artist's paintbrush" (13c., Modern French pinceau), from Latin penicillus "painter's brush, hair-pencil," literally "little tail," diminutive of peniculus "brush," itself a diminutive of penis "tail" (see penis). Small brushes formerly were used for writing before modern lead or chalk pencils; meaning "graphite writing implement" apparently evolved late 16c. Derogatory slang pencil-pusher "office worker" is from 1881; pencil neck "weak person" first recorded 1973.
penicillin (n.)youdaoicibaDictYouDict
1929, coined in English by Alexander Fleming (1881-1955), who first recognized its antibiotic properties, from Modern Latin Penicillium notatum (1867), the name of the mould from which it was first obtained, from Latin penicillus "paintbrush" (see pencil (n.)), in reference to the shape of the mould cells.