also side-show, 1855, "minor exhibition alongside or near a principal one," apparently a coinage of P.T. Barnum's, from side (adj.) + show (n.). Hence, any diversion or distracting event.
instruction is not an educational sideshow
sidelong
sideman
sidenote
sidereal
side-saddle
sideshow
sidestep
side-swipe
side-table
sidetrack
sidewalk