fiveyoudaoicibaDictYouDict[five 词源字典]
five: [OE] Five is one of a general Indo-European family of words signifying ‘five’. It goes back ultimately to Indo-European *pengke, which also produced Greek pénte (source of English pentagon [16], pentecost [OE] – literally ‘fiftieth day’ – pentagram [19], etc), Sanskrit panca (source of English punch ‘spiced drink’), and Latin quīnque. In due course this under-went a phonetic transformation to *pempe, which was the direct ancestor of prehistoric Germanic *fimfi. This led on in its turn to German fünf, Dutch vijf. Swedish and Danish fem, and English five.
=> finger, fist, pentagon, punch[five etymology, five origin, 英语词源]
five (n.)youdaoicibaDictYouDict
Old English fif "five," from Proto-Germanic *fimfe (cognates: Old Frisian fif, Old Saxon fif, Dutch vijf, Old Norse fimm, Old High German funf, Gothic fimf), from PIE *penkwe- (cognates: Sanskrit panca, Greek pente, Latin quinque, Old Church Slavonic peti, Lithuanian penke, Old Welsh pimp). The sound shift that removed the *-m- is a regular development involving Old English, Old Frisian, and Old Saxon (as in thought, from stem of think; couth from *kunthaz; us from *uns).

Five-and-ten (Cent Store) is from 1880, American English, with reference to prices of goods for sale. Five-star (adj.) is from 1913 of hotels, 1945 of generals. Slang five-finger discount "theft" is from 1966. The original five-year plan was 1928 in the U.S.S.R. Five o'clock shadow attested by 1937.
[under picture of a pretty girl] "If I were a man I'd pay attention to that phrase '5 O'Clock Shadow.' It's that messy beard growth which appears prematurely about 5 P.M." [Advertisement for Gem razors and blades, Life," May 9, 1938]