landing vs touchdown

landing and touchdown both are nouns.

Word	Noun	Adjective	Verb	Adverb
landing	Yes	No	No	No
touchdown	Yes	No	No	No

As nouns, touchdown is a hyponym of landing; that is, touchdown is a word with a more specific, narrower meaning than landing:

landing: the act of coming down to the earth (or other surface)
touchdown: a landing (as the wheels touch the landing field); especially of airplanes

Other hyponyms of landing include aircraft landing, airplane landing, splashdown.

landing (noun)	touchdown (noun)
the act of coming to land after a voyage	a score in American football; being in possession of the ball across the opponents' goal line
the act of coming down to the earth (or other surface)	a landing (as the wheels touch the landing field); especially of airplanes
structure providing a place where boats can land people or goods
an intermediate platform in a staircase