Yog योग

A Sanskrit dictionary defines Yog as

(1) Joining, uniting

(2) Union

(3) Contact, touch, connection

(23) Deep and abstract meditation, concentration of the mind, contemplation of the Supreme Spirit

(24) The system of philosophy established by Paatanjali (where AA is pronounced as A in Bata and A is pronounced as U in But), which is considered to be the second division of the Saankhya philosophy, but is practically reckoned as a separate system.  The chief aim of the Yog philosophy is to teach the means by which the human soul may be completely united with the Supreme Spirit and thus secure absolution; and deep abstract meditation is laid down as the chief means of securing this end, elaborate rules being given for the proper practice of such Yog or concentration of mind)

(30) Devotion, pious seeking after God.

Yoga is the popular spelling that we generally see in print.  However, we have chosen Yog because it offers a relatively closer pronunciation to the original Sanskrit word. 

Readers tend to pronounce a Sanskrit word as they see it written in English.  Yoga prompts them to pronounce it incorrectly.  A in the end of Yoga gives them the impression that it should be pronounced as A in Bata.  There is nothing in the spelling of Yoga to indicate that A should be pronounced as U in But. 

Over the passage of time, Yoga has encouraged the humankind to pronounce it in a distorted manner. 

This is particularly unfortunate for the language Sanskrit, whose phonetics are highly scientific.