layby vs rest area

layby and rest area both are nouns.

Word	Noun	Adjective	Verb	Adverb
layby	Yes	No	No	No
rest area	Yes	No	No	No

As nouns, layby and rest area are synonyms defined as:

layby and rest area: designated paved area beside a main road where cars can stop temporarily

Other synonyms of layby include lay-by, pull-off, rest stop.

layby (noun)	rest area (noun)
designated paved area beside a main road where cars can stop temporarily	designated paved area beside a main road where cars can stop temporarily