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Online Etymology Dictionary - Cite This Source - Share This
penis
1676, perhaps from Fr. pénis or directly from L. penis "penis," earlier "tail" (cf. Eng. tail in both senses, the sexual one slang), from PIE *pes-/*pesos- "penis" (cf. Skt. pasas-, Gk. peos, posthe "penis," probably also O.E. fæsl "progeny, offspring," O.N. fösull, Ger. Fasel "young of animals, brood"). The proper plural is penes. The adj. is penial. In psychological writing, penis envy is attested from 1924.
Online Etymology Dictionary, © 2001 Douglas Harper
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I was looking up something in the online dictionary, came across this and thought I would, as suggested by the author, share it with you. I noted the correct plural form is 'penes', not 'penii'. Mind you, 'fösull' is a good name - it has such wonderful connotations!