All 5 Uses

rational
in
The Hunt for Red October
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That would be the only rational thing for them to do, and while I do not regard the Soviets as entirely rational by our standards, they are rational by their own.†
Chpt 6.

rational = reasonable
That would be the only rational thing for them to do, and while I do not regard the Soviets as entirely rational by our standards, they are rational by their own.†
Chpt 6.
That would be the only rational thing for them to do, and while I do not regard the Soviets as entirely rational by our standards, they are rational by their own.†
Chpt 6.
Even so, something that could neither be seen nor felt was invading his body, and no rational person would be happy with that.†
Chpt 9. *
He had never really thought about what makes a defector, figuring that there were enough things happening on the other side of the Iron Curtain to make any rational person want to take whatever chance he got to run west.†
Chpt 11.

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.