ir- vs un-

ir-

prefix
  • Used for expressing negation; not 

un-

prefix
  • absent; lacking; not; negative 

  • do the opposite of, reverse (a specified action) 

  • contrary to or contrasted against traditional norms; unconventional; alternative 

  • Used to form temporary names of elements (such as unbiunium) whose existence has been predicted, and have not yet been given a trivial name. 

  • deprive of, release from, free from, remove from, extract from 

  • intensifying a verb that already suggests opposition or removal 

  • not 

  • Used to form large numbers as the first in the sequence. 

How often have the words ir- and un- occurred in a corpus of books? (source: Google Ngram Viewer )