side-by-side

• side by side

From side + by + side.

side-by-side (not comparable)

1. Adjacent.
   • 2013 June 1, “Ideas coming down the track”, in The Economist, volume 407, number 8838, page 13 (Technology Quarterly):

     A “moving platform” scheme […] is more technologically ambitious than maglev trains even though it relies on conventional rails. Local trains would use side-by-side rails to roll alongside intercity trains and allow passengers to switch trains by stepping through docking bays.

• This hyphenated spelling is usually used before a noun it modifies, whereas the unhyphenated spelling is used after a noun it modifies.