pigeon keeping vs sideline

pigeon keeping and sideline both are nouns.

Word	Noun	Adjective	Verb	Adverb
pigeon keeping	Yes	No	No	No
sideline	Yes	No	Yes	No

As nouns, sideline is a hypernym of pigeon keeping; that is, sideline is a word with a broader meaning than pigeon keeping:

Other hypernyms of pigeon keeping include avocation, by-line, hobby, pursuit, spare-time activity.

pigeon keeping (noun)	sideline (noun)
the art and science of breeding domestic pigeons.	an auxiliary activity
	an auxiliary line of merchandise
	a line that marks the side boundary of a playing field

pigeon keeping (verb)	sideline (verb)
	remove from the center of activity or attention; place into an inferior position