first aid vs tending

first aid and tending both are nouns.

Word	Noun	Adjective	Verb	Adverb
first aid	Yes	No	No	No
tending	Yes	Yes	No	No

As nouns, tending is a hypernym of first aid; that is, tending is a word with a broader meaning than first aid:

first aid: emergency care given before regular medical aid can be obtained
tending: the work of providing treatment for or attending to someone or something

Other hypernyms of first aid include aid, attention, care.

first aid (noun)	tending (noun)
emergency care given before regular medical aid can be obtained	the work of providing treatment for or attending to someone or something

first aid (adjective)	tending (adjective)
	(usually followed by `to') naturally disposed toward