Wiktionary
side-to-side
a. Moving horizontally, from one side to another and back.
WordNet
side-to-side
adj. alternately left and right with respect to a central point; "the side-to-side motion of the boat"
Usage examples of "side-to-side".
But to Tad, although the basket had no up-and-down weight, it would still have a certain amount of side-to-side mass and momentum.
The side-to-side changes in the electric field propagate from one tape to the other as a wave traveling at the speed of light.
She had wrenched the cart free from its paramour, next in the line, and she was wheeling it down the nearest aisle, a side-to-side hipslung movement that was all sinuousness and the music of silks on silks.