Side by side and Sidelong

Side by side adjective - Nearest in space or position; immediately adjoining without intervening space.

Sidelong and side by side are semantically related In some cases you can use "Sidelong" instead the phrase "Side by side" as an adverb or an adjective.

Sidelong adverb - On the side.

Side by side and sidelong are semantically related in exteriority topic. Sometimes you can use "Side by side" instead an adverb "Sidelong".