-alis

of, relating to

Forms

-alis
-aris — Latin variant especially used when the stem already contained l, avoiding a repeated l sound.
-al — English ending borrowed through French or directly from Latin.
-ar — English ending continuing Latin -aris.

Origin

An older Latin adjective-forming suffix; its more remote ancestry is uncertain.

Note

Expresses a relationship without specifying its kind: material, place, purpose, and other connections are possible.

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adjective

irrational

ih-RASH-uh-nuhl/ɪˈræʃənl/

Not based on reason or sound judgment.

His irrational choice avoids the sturdy bridge in favor of a muddy detour.

An adult irrationally refuses a sturdy bridge and instead attempts an obviously impractical detour through shallow mud, safe nonviolent scene.

Etymology

irLatinnot; without

+rationLatinreckoning, reasoning, or account

+alLatinof, relating to

The pieces mean not belonging to reason. Initially describing beings thought to lack the power of reasoning, irrational came to describe ideas or conduct that fail to follow reason.

In context

TED-Ed1:46

irrational decisions, not like falling in love or bungee jumping off a cliff, but logical fallacies that can easily be proven wrong.

The psychology behind irrational decisions - Sara Garofalo

More examples

The fear was irrational but persistent.
She challenged the irrational conclusion.
Their spending became increasingly irrational.

Forms

irrational

Similar words

unreasonable: Unreasonable can concern unfair demands as well as faulty reasoning.
illogical: Illogical specifically concerns faulty reasoning rather than emotional unreasonableness.