The prefix vi- is seen in some commonly used Pali & Sanskrit Buddhist terms;  such as vimala, vinaya, vinnana/vijnana, visuddha/vishuddha, vihara, and vipassana/vipashyana.  It is a cognate of the common English prefix dis- [or de-].  

Note that most English speakers consider dis-/de- to be a negation. Actually, it simply means ‘apart.’  In many cases, this implies a kind of negation. However, there are three or four main functions; and many times there is no negation.   I go with three:

A Reversal or Removal. This is similar to a negation. An example in English is disappear; to cease to appear. Another is disconnect; to end a connection. Disengage, disservice,  and defuse are other examples in which dis-  serves to reverse the meaning of the base word.  An example of this function is seen in the Buddhist terms viraga and  vimala.

To sunder, sever, divide,  separate, or take ‘apart:’ Sometimes this is sort of like a negations, as in the word dismember — to cut or tear off or part. At other times, it simply kind of sorts things out, as in delineate. Disseminate is another example in which dis- means to  divide up, as is discourse.  This kind of function for vi-  is seen in the Buddhist terms vinaya, vihara,  and vinnana / vijnana.

An Intensifier: This use of dis- in English, or vi- in Pali or Sanskrit, does not change the meaning of the root word; it sets the use of the word ‘apart’ from its common usage. The best example in English ins disgruntled. What were we before we became disgruntled? Were we gruntled? The answer is yes.  Gruntle is an old verb that meant to groan,  grunt, or grumble.   So, gruntled meant that one was malcontented.  Disgruntled means to be utterly discontented, an intensive of gruntled.  There is also the verb debar; which means virtually  the same thing as the verb bar;  but might imply a more official or permanent prohibition. Also, disannul intensifies annul. The vi- in the Buddhist terms vipassana / vipashyana, and  visuddha / vishuddha is an intensifier. By the way,  em-,  en-, ex-, il-, in-, and ir- are other examples are prefixes than can act like negations; but are also used as intensifiers.

Finally, looking at etymologies  has not only helped me understand Buddhist terms, it has also helped me better appreciate the nuances of my own English language.   Sometimes, the prefix dis- can mean different things in the same word, depending on context. An example is discern. The ‘cern; part is from a root that means ‘to sift.’  Discern can mean to see , detect, or recognize intently or clearly;  in that case dis- is an intensive.  However, discern can  also mean to identify differences or discriminate, in that cases dis-  serves to indicate division or separation.