plural form vs Ludi Saeculares

plural form and Ludi Saeculares both are nouns.

Word	Noun	Adjective	Verb	Adverb
plural form	Yes	No	No	No
Ludi Saeculares	Yes	No	No	No

plural form (noun)	Ludi Saeculares (noun)
the form of a word that is used to denote more than one	the centennial rites and games of ancient Rome that marked the commencement of a new generation (100 years representing the longest life in a generation); observances may have begun as early as the 5th century BC and lasted well into the Christian era