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1.
  
     (a) Not endowed with reason.
   
     (b) Affected by loss of usual or normal mental clarity; incoherent, as from shock.
  
     (c) Marked by a lack of accord with reason or sound judgment: an irrational dislike.
  
2.
  
     (a) Being a syllable in Greek and Latin prosody whose length does not fit the metric pattern.
  
     (b) Being a metric foot containing such a syllable.
  
3.  Mathematics. Of or relating to an irrational number.
  
  
Absolutely brilliant, Shoeboy.  Would it have been possible for you to have selected a single, better word?
 
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