Meaning

noun an integer or a fraction

adjective consistent with or based on or using reason

adjective of or associated with or requiring the use of the mind

originFrom Old French rational, from Medieval Latin rationale (“a pontifical stole, a pallium, an ornament worn over the chasuble”), neuter of Latin rationalis (“rational”), for which see the first etymology. Translation of λογεῖον (logeîon) or perhaps λόγιον (lógion, “oracle”) in the Septuagint version of Exodus 28.

Etymology from Wiktionary, CC BY-SA 3.0