[1] : The Collaborative International Dictionary of English v.0.48

eighteenth \eight"eenth`\, a. from eighteen.
   1. next in order after the seventeenth.
      1913 webster

   2. consisting of one of eighteen equal parts or divisions of
      a thing.
      1913 webster
see also:
eighteen 

[2] : The Collaborative International Dictionary of English v.0.48

eighteenth \eight"eenth`\, n.
   1. the quotient of a unit divided by eighteen; one of
      eighteen equal parts or divisions.
      1913 webster

   2. the eighth after the tenth.
      1913 webster

[3] : WordNet (r) 2.0

eighteenth
     adj : coming next after the seventeenth in position syn: 18th
     n : position 18 in a countable series of things
see also:
18th 

Eighteenth >> E Words
Eighteenth, definition of term: Eighteenth
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