Definition of Intercession

 The verbal noun of shafa´au, shafa´atan is derived from ash-shaf´ (even), which is merging one thing with another and the opposite of which is witr (odd).

Ash-Shafaa´ah is asking for good on behalf of someone else. It is called shafa´ah because the person was alone in his request at the beginning and when someone else joins him in the request alongside him, they become shaf´an i.e. two.