じゃんけんぽん

Unknown. The initial portion is likely from 石拳(しゃっけん) (shakken, literally “stone fist”) or similar; see じゃん拳(けん) (janken). The final portion may be onomatopoeic; compare ボーン (bōn, “kaboom!”), パンパン (panpan, “bang bang!”). Compare also はい (hai, “go! start!”), ほい (hoi, interjection used to call for attention). Attested from the early twentieth century.^[1]

• (Tokyo) じゃんけんぽん (Nakadaka – )
• IPA^(key):

じゃんけんぽん • (jankenpon) 

1. used to initiate a round of rock paper scissors and synchronize the start of the game

   Synonyms: じゃんけんぽい (jankenpoi), そーれんぜぃが (sōrenzēga)

   • 1903, Monbusho , Jinjō shogakko dokuhon 7.1 [Common elementary school reader]:

     みんなが、いっしょに、おにごとあそび。おにをきめるよ。『じゃん、けん、ぽん』

     Minna ga, issho ni, onigoto asobi. Oni o kimeru yo. “jan, ken, pon”

     Everyone, let’s play tag together. Let’s decide who is it. “jan, ken, pon”

• あいこでしょ (aiko desho, interjection used to play again if players show the same gesture, literally “a tie, isn’t it”)
• あいこでほい (aiko de hoi, interjection used to play again, literally “it’s a tie, hey!”)

じゃんけんぽん • (jankenpon) 

1. the cry used to initiate rock paper scissors
2. synonym of じゃん拳 (“rock paper scissors”)

• → Portuguese: joquempô
• → Tagalog: dyak en poy