by-line vs credit line

by-line and credit line both are nouns.

Word	Noun	Adjective	Verb	Adverb
by-line	Yes	No	No	No
credit line	Yes	No	No	No

As nouns, by-line and credit line are synonyms defined as:

by-line and credit line: a line giving the name of the writer of a story or article

by-line (noun)	credit line (noun)
an auxiliary activity	a line giving the name of the writer of a story or article
a line giving the name of the writer of a story or article	the maximum credit that a customer is allowed