From mid- +‎ set.

midset (not comparable)

1. (music) In the middle of a set, in the middle of a gig.
   • 2009 March 17, Jon Caramanica, “Surfing Along a Foamy Wave, Constantly Changing but Ever Cynical”, in New York Times‎^[1]:

     And the band appears comfortable with its pop instincts: a pair of new songs, played midset, were even frothier and looser than its album.

• MiSTed, demist, demits, midest, misted, smited