1 : with one side facing forward

We had to turn sideways to let them through the crowded hallway.

crabs walking sideways along the beach

2 : to or toward the right or left side

Helicopters can fly up, down, forward, backward, and sideways.

She fell sideways and landed on her shoulder.

I looked sideways at him to see if he was smiling.

— sideways adjective

sideways movement/glance