fivesyoudaoicibaDictYouDict[fives 词源字典]
"A game, played especially in the UK, in which a ball is hit with a gloved hand or a bat against the walls of a court with three walls ( Eton fives) or four walls ( Rugby fives)", Mid 17th century: plural of five used as a singular noun; the significance is unknown.[fives etymology, fives origin, 英语词源]