side by side adv. 1. One beside the other in a row. 
 Alice's dolls were lined up side by side on the window seat.
 Alice's dolls were lined up side by side on the window seat.  Charles and John are neighbors; they live side by side on Elm Street. Compare:
 Charles and John are neighbors; they live side by side on Elm Street. Compare: SHOULDER TO SHOULDER. 
2. Close together. 
 The two boys played side by side all afternoon.
 The two boys played side by side all afternoon.  [TahlilGaran] English Idioms Dictionary ▲