martial art vs self-defence

martial art and self-defence both are nouns.

Word	Noun	Adjective	Verb	Adverb
martial art	Yes	No	No	No
self-defence	Yes	No	No	No

As nouns, self-defence is a hypernym of martial art; that is, self-defence is a word with a broader meaning than martial art:

martial art: any of several Oriental arts of weaponless self-defense; usually practiced as a sport
self-defence: the act of defending yourself

Other hypernyms of martial art include self-defense, self-protection.

martial art (noun)	self-defence (noun)
any of several Oriental arts of weaponless self-defense; usually practiced as a sport	the act of defending yourself