steamship company vs steamship line

steamship company and steamship line both are nouns.

Word	Noun	Adjective	Verb	Adverb
steamship company	Yes	No	No	No
steamship line	Yes	No	No	No

As nouns, steamship company and steamship line are synonyms defined as:

steamship company and steamship line: a line responsible for the operation of a fleet of steamships

steamship company (noun)	steamship line (noun)
a line responsible for the operation of a fleet of steamships	a line responsible for the operation of a fleet of steamships