wildcat strike vs work stoppage

wildcat strike and work stoppage both are nouns.

Word	Noun	Adjective	Verb	Adverb
wildcat strike	Yes	No	No	No
work stoppage	Yes	No	No	No

As nouns, work stoppage is a hypernym of wildcat strike; that is, work stoppage is a word with a broader meaning than wildcat strike:

wildcat strike: a strike undertaken by workers without approval from the officials of their union
work stoppage: a group's refusal to work in protest against low pay or bad work conditions

Other hypernyms of wildcat strike include strike.

wildcat strike (noun)	work stoppage (noun)
a strike undertaken by workers without approval from the officials of their union	a group's refusal to work in protest against low pay or bad work conditions