side by side vs adjacent

side by side and adjacent both are adjectives.

Word	Noun	Adjective	Verb	Adverb
side by side	No	Yes	No	No
adjacent	No	Yes	No	No

As adjectives, side by side and adjacent are synonyms defined as:

side by side and adjacent: nearest in space or position; immediately adjoining without intervening space

Other synonyms of side by side include next.

side by side (adjective)	adjacent (adjective)
nearest in space or position; immediately adjoining without intervening space	nearest in space or position; immediately adjoining without intervening space
closely related or associated	having a common boundary or edge; abutting; touching
	near or close to but not necessarily touching