penyoudaoicibaDictYouDict[pen 词源字典]
pen: English has three words pen. The oldest, ‘enclosure’ [OE], is something of a mystery term. It has no known relatives in the other European languages, and even in English it is not unequivocally found in its current sense until the 14th century. Pent [16], as in ‘pent up’, originated in the past participle of the verb pen. The earliest writing implements known as ‘pens’ were of course made from feathers, and so it is not surprising that the word pen [13] comes from a word that meant ‘feather’.

This was Latin penna, source also of English pennon [14] and a distant relative of English feather. It entered English via Old French penne. Pen ‘female swan’ [16] is of unknown origin.

=> pent; feather, pennon[pen etymology, pen origin, 英语词源]
pen (n.3)youdaoicibaDictYouDict
slang, "prison," 1884, shortening of penitentiary; earlier use (1845) probably is a figurative extension of pen (n.2).
pen (n.1)youdaoicibaDictYouDict
"writing implement," late 13c., from Old French pene "quill pen; feather" (12c.) and directly from Latin penna "a feather, plume," in plural "a wing," in Late Latin, "a pen for writing," from Old Latin petna, pesna, from PIE *pet-na-, suffixed form of root *pet- "to rush; to fly" (see petition (n.)).

Latin penna and pinna "a feather, plume;" in plural "a wing;" also "a pinnacle; battlement" (see pin (n.)) are treated as identical in Watkins, etc., but regarded as separate (but confused) Latin words by Tucker and others, who derive pinna from PIE *spei- "sharp point" (see spike (n.1)) and see the "feather/wing" sense as secondary.

In later French, this word means only "long feather of a bird," while the equivalent of English plume is used for "writing implement," the senses of the two words thus are reversed from the situation in English. Pen-and-ink (adj.) is attested from 1670s. Pen name is recorded from mid-19c.
pen (v.2)youdaoicibaDictYouDict
"to enclose in a pen," c. 1200, from Old English *pennian, from the source of pen (n.2). Related: Penned; penning.
pen (n.2)youdaoicibaDictYouDict
"enclosure for animals," Old English penn, penne, "enclosure, pen, fold," of uncertain origin, perhaps related to Old English pinn "pin, peg" (see pin (n.)) on notion of a bolted gate or else "structure made of pointed stakes."
pen (v.1)youdaoicibaDictYouDict
late 15c., from pen (n.). Related: Penned; penning.