penta-youdaoicibaDictYouDict[penta- 词源字典]
word-forming element meaning "five, containing five," from Greek penta- (before a vowel pent-), comb. form of pente "five," related to Aeolian pempte (see five), with -a- by analogy of hepta-, ennea-, deka-.[penta- etymology, penta- origin, 英语词源]