This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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n. A member of a jazz band who is not the leader or a featured soloist.

n. A soloist playing with a band or group of which he is not a regular member

"At 40, Mr. Potter is probably still better known as a sideman most famously with bassist Dave Holland, but there's no doubt that he's assembled a group and a musical concept that's worthy of his formidable technique."

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