Mid 19th century; earliest use found in Phytologist. From classical Latin rārissimē, lit. ‘very rarely’, superlative of rārō rarely, seldom from rārus + -ō, suffix forming adverbs.
Definition of rarissime in US English:
rarissime
adjective
Extremely rare.
Origin
Mid 19th century; earliest use found in Phytologist. From classical Latin rārissimē, lit. ‘very rarely’, superlative of rārō rarely, seldom from rārus + -ō, suffix forming adverbs.