All 4 Uses

rational
in
Anna and the French Kiss
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I'm determined to speak rationally in his presence.†
p. 24.1
It's not fair, not rational, for me to be this angry with him, but I can't help it.†
p. 164.1

rational = reasonable
Think about it, she'll get dolled up in one of those satin monstrosities no rational girl would ever wear, and they'll take one of those awful pictures—†
p. 305.7 *
I hate that every time we meet, he's with a different woman, and I hate that they all think he's this wonderful, charming bloke, when really he's a vicious bastard who'd sooner humiliate me than discuss my education rationally.†
p. 351.3

Definitions:

(1) (rational as in: rational behavior)
reasonable, able to think clearly, or based on logic rather than emotion
(2) (meaning too rare to warrant focus)
More rarely, rational numbers in mathematics are numbers that can be expressed as a fraction consisting of only an integer in the numerator and denominator. For example, 1/3 is a rational number while pi is an irrational number.