ab initio

ab in·​i·​tio | \ ˌab-ə-ˈni-shē-ˌō How to pronounce ab initio (audio) \

Definition of ab initio

: from the beginning

Starting Things With Ab Initio

We'll tell you right from the beginning where ab initio comes from. This adverb was adopted at the beginning of the 17th century directly from Latin, where it translates as "from the beginning." (Initio is a form of the noun initium, meaning "beginning," which gave rise to such English words as initial, initiate, and initiative.) Ab initio most frequently appears in legal contexts, but it is not surprising to find it used outside of the courtroom. The phrase is also used as an adjective meaning "starting from or based on first principles" (as in "predicted from ab initio calculations").

Examples of ab initio in a Sentence

Recent Examples on the Web What McConnell needed to do, for his argument to establish its conclusions, was to provide independent grounds of some kind for ruling out Interpretation B ab initio. Jason Lee Steorts, National Review, 15 May 2021 Moreover, the Executive Order exceeds the President’s authority and is therefore ultra vires and void ab initio. Eriq Gardner, Billboard, 4 Sep. 2020

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'ab initio.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of ab initio

1600, in the meaning defined above

History and Etymology for ab initio

Latin ab initiō

Learn More About ab initio

Time Traveler for ab initio

Time Traveler

The first known use of ab initio was in 1600

See more words from the same year

Listen to Our Podcast About ab initio

Dictionary Entries Near ab initio


ab initio

ab intra

See More Nearby Entries 

Statistics for ab initio

Cite this Entry

“Ab initio.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/ab%20initio. Accessed 16 May. 2022.

Style: MLA
MLACheck Mark Icon ChicagoCheck Mark Icon APACheck Mark Icon Merriam-WebsterCheck Mark Icon

More Definitions for ab initio

ab initio

ab ini·​tio | \ ˌab-ə-ˈni-shē-ˌō, ˌäb-i-ˈnē-tē-ˌō How to pronounce ab initio (audio) \

Legal Definition of ab initio

: from the beginning a contract found to be void ab initio

History and Etymology for ab initio


More from Merriam-Webster on ab initio

Britannica English: Translation of ab initio for Arabic Speakers


Test Your Vocabulary

Eponyms: Words Named After People

True or False

Test your knowledge - and maybe learn something along the way.

Universal Daily Crossword

A daily challenge for crossword fanatics.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!