steamship line vs steamship company

steamship line and steamship company both are nouns.

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

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

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

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