三味線

a Japanese stringed instrument played by plucking, vaguely similar to a banjo

short for 三味線草 (shamisen-gusa): the shepherd's purse, Capsella bursa-pastoris

from 三味線を弾く (shamisen o hiku, literally “to play the shamisen”): words or actions intended to deceive one's opponent in a game or competition

(academia, slang) a grade of 甲 (kō, highest mark, equivalent to an “A” in US schools) (from the vague visual similarity between the character 甲 and the shape of the shamisen)