also: まるメンコ
noun
round menko card
A round variant of menko, a traditional Japanese card-flipping game. The term refers specifically to the round-shaped cards used in the game.
See also: 面子 (めんこ)
昔、子供たちは丸面子を地面に叩きつけて遊んだ。
In the old days, children played by slamming round menko cards onto the ground.
面子 is the general term for menko cards, which are usually rectangular. 丸面子 specifically refers to the round variant.
Compound of 丸 (まる, 'round') and 面子 (めんこ, 'menko card'). The exact origin of めんこ is uncertain, but it refers to a traditional Japanese card game.