reductio ad absurdum

UK: /rɪˈdʌktɪəʊ æd æbˈsɜːdəm/

US: (ri duk′tē ō′ ad′ ab sûr′dəm, -zûr′-, -shē ō′)

WordReference Random House Unabridged Dictionary of American English © 2025

re•duc•ti•o ad ab•sur•dum  (ri duk′tē ō′ ad′ ab sûr′dəm, -zûr′-, -shē ō′), [Logic.]

1. Philosophy a reduction to an absurdity;
   the refutation of a proposition by demonstrating the inevitably absurd conclusion to which it would logically lead.

• Latin reductiō ad absurdum
• 1735–45

Collins Concise English Dictionary © HarperCollins Publishers::

reductio ad absurdum / rɪˈdʌktɪəʊ æd æbˈsɜːdəm/ noun

1. a method of disproving a proposition by showing that its inevitable consequences would be absurd
2. a method of indirectly proving a proposition by assuming its negation to be true and showing that this leads to an absurdity
3. application of a principle or proposed principle to an instance in which it is absurd

Etymology: Latin, literally: reduction to the absurd