sightseeing vs rubber-necking

sightseeing and rubber-necking both are nouns.

Word	Noun	Adjective	Verb	Adverb
sightseeing	Yes	No	No	No
rubber-necking	Yes	No	No	No

As nouns, sightseeing and rubber-necking are synonyms defined as:

sightseeing and rubber-necking: going about to look at places of interest

sightseeing (noun)	rubber-necking (noun)
going about to look at places of interest	going about to look at places of interest