pastime vs by-line

pastime and by-line both are nouns.

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

As nouns, by-line is a hyponym of pastime; that is, by-line is a word with a more specific, narrower meaning than pastime:

pastime: a diversion that occupies one's time and thoughts (usually pleasantly)
by-line: an auxiliary activity

Other hyponyms of pastime include avocation, hobby, pursuit, sideline, spare-time activity.

pastime (noun)	by-line (noun)
a diversion that occupies one's time and thoughts (usually pleasantly)	an auxiliary activity
	a line giving the name of the writer of a story or article