Ab initio Definition & Meaning – Merriam-Webster

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”).