Latin ab initiōabfrominitiōablative ofinitiumbeginning
American Heritage Dictionary of the English Language, 5th Edition
From Latinab (“from”) + initiō, ablative singular of initium (“beginning”).
Webster's New World College Dictionary, 5th Edition
Ab-initio Sentence Examples
Both experimental work and ab-initio calculations agree that the most stable form is the ammonium ion pair species.
Most ab initio groups quickly become very close-knit since students see each other almost every day.
The marriage was declared invalid ab initio either on the ground of Anne's precontract with Lord Percy or more probably on the ground of the affinity established between Henry and Anne by Henry's previous relations with Mary Boleyn.
Working on these lines, and attaching special importance to common descent, naturalists applied the term with more and more precision, until Linnaeus, in his Philosophia botanica, gave the aphorism, "species tot sunt diversae, quot diversae formae ab initio sunt creatae" - "just so many species are to be reckoned as there were forms created at the beginning."
They describe an English speaking ab initio student of German who exhibited an unusually strong tendency to use word coinage and lexical innovation.