death vs megadeath

death and megadeath both are nouns.

Word	Noun	Adjective	Verb	Adverb
death	Yes	No	No	No
megadeath	Yes	No	No	No

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

death (noun)	megadeath (noun)
the act of killing	the death of a million people
the event of dying or departure from life
the permanent end of all life functions in an organism or part of an organism
the absence of life or state of being dead
a final state
the time when something ends
the time at which life ends; continuing until dead