The phrase "a side piece" is correct and usable in written English.
It is typically used to refer to a person with whom someone is having a romantic or sexual relationship outside of their primary relationship.
Example: "He was seeing her on the side as a side piece, while still being committed to his long-term girlfriend."
Alternatives: "an affair partner" or "a mistress".
Just as Mr. Leuschen was teaming up with Carlyle in 2000, he got a side piece of business from a neighbor, Barrett Wissman, an entrepreneur who had a ranch next to his in Red Lodge, Mont., and who managed money for the Hunt family of Texas.
It's refreshing to see intimate friendships between women treated as the main event, instead of a side piece to the heterosexual action.
Dadoes are used in joining two pieces of wood at 90 degrees, such as adding a kitchen cabinet shelf to a side piece.
Alexandra was included as part of a small side piece on volunteering in which the paper said she, along with Rachel Stevens and Aldo Zilli, would be volunteering by serving up fish and chips at a Soho restaurant.
Back in the 70s, Eli's was a premier Oakland blues joint before its namesake was gunned down (in the bar) by a jealous side piece.
Cut out the piece and use that piece to cut out a second side piece.
Cut one length for the antler stem, then a much smaller side piece for the branching off part of the antler.
6. Designed by Emaf Progetti for Zanotta, the Alfa Bed has a headboard that includes a pair of removable side pieces, or one side piece and a pouf (as shown).
Translation devices will be even more useful, he said, in 5 to 10 years, when the camera is in the side piece of a person's glasses with the display in the top edge.
Cut the remaining side piece to a width of 5 inches, and fold in half lengthwise Sew along the length of this piece.
Sew straight across the top edge of the top side piece with a 1/2 inch (1.25 cm) seam allowance, joining it to the main body piece in the process.
