sideman
...that a sideman is a professional musician who is hired to perform or record with a group of which he is not formally a member?
...that a <b id="mwBCw"><a href="./Sideman" id="mwBC0" rel="mw:WikiLink" title="Sideman">sideman</a></b> is a professional <a href="./Musician" id="mwBC4" rel="mw:WikiLink" title="Musician">musician</a> who is hired to perform or record with a <a class="mw-redirect" href="./Musical_band" id="mwBC8" rel="mw:WikiLink" title="Musical band">group</a> of which he is not formally a member?