1. 
   opr
   abbreviation: operate, also, operator
   Found op http://www.apscharts.com/abbrev.html
   
   
2. 
   OPR
   Over Pressure Relief
   Found op http://www3.sympatico.ca/dhaughey/j1930.htm
   
   
3. 
   OPR
   Old Parochial Register of the Church of Scotland.
   Found op http://www.brockett.info/Level1/Glossary.htm
   
   
4. 
   opr
   1) Abbreviation
   Found op operate, also, operator
   
   

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