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
a sideways movement/glance