sit-down vs work stoppage

sit-down and work stoppage both are nouns.

Word	Noun	Adjective	Verb	Adverb
sit-down	Yes	No	No	No
work stoppage	Yes	No	No	No

As nouns, work stoppage is a hypernym of sit-down; that is, work stoppage is a word with a broader meaning than sit-down:

sit-down: a strike in which workers refuse to leave the workplace until a settlement is reached
work stoppage: a group's refusal to work in protest against low pay or bad work conditions

Other hypernyms of sit-down include strike.

sit-down (noun)	work stoppage (noun)
a strike in which workers refuse to leave the workplace until a settlement is reached	a group's refusal to work in protest against low pay or bad work conditions