railroad tie vs crosstie

railroad tie and crosstie both are nouns.

Word	Noun	Adjective	Verb	Adverb
railroad tie	Yes	No	No	No
crosstie	Yes	No	No	No

As nouns, railroad tie and crosstie are synonyms defined as:

railroad tie and crosstie: one of the cross braces that support the rails on a railway track

Other synonyms of railroad tie include sleeper, tie.

railroad tie (noun)	crosstie (noun)
one of the cross braces that support the rails on a railway track	one of the cross braces that support the rails on a railway track