ceremony vs lustrum

ceremony and lustrum both are nouns.

Word	Noun	Adjective	Verb	Adverb
ceremony	Yes	No	No	No
lustrum	Yes	No	No	No

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

ceremony: the proper or conventional behavior on some solemn occasion
lustrum: a ceremonial purification of the Roman population every five years following the census

ceremony (noun)	lustrum (noun)
the proper or conventional behavior on some solemn occasion	a ceremonial purification of the Roman population every five years following the census
any activity that is performed in an especially solemn elaborate or formal way	a period lasting five years
a formal event performed on a special occasion