All 4 Uses

irrational
in
My Name is Legion
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Now it was sinister, bringing a fear that was none the less real for my knowing it to be irrational, to the accompaniment of sensory distortions that must have caused me to reel as I ran.†
Part 2 *

irrational = unreasonable
I had the sudden, irrational feeling that she somehow knew all about me and was playing games at that moment.†
Part 2
It went irrational once more, indicated that it was heading for a landing on Uranus itself, and that was it.†
Part 3
From what we know of the Hangman, the last we heard of it, it had become irrational.†
Part 3

Definitions:

(1) (irrational)
not reasonable
(2) (meaning too rare to warrant focus)
More rarely, irrational numbers in mathematics are numbers that cannot be expressed as a fraction consisting of only an integer in the numerator and denominator. For example, pi is an irrational number while 1/3 is rational.