Mid 19th century; earliest use found in Edward Edwards (1812–1886), librarian and writer. From classical Latin rāriora, neuter plural of rārior rarer from rārus + -ior.
Definition of rariora in US English:
rariora
noun
Treated as plural. Rare books.
Origin
Mid 19th century; earliest use found in Edward Edwards (1812–1886), librarian and writer. From classical Latin rāriora, neuter plural of rārior rarer from rārus + -ior.