The Collaborative International Dictionary of English v.0.48:

Sixteen \Six"teen`\, a. [AS. sixt?ne, sixt?ne. See Six, and
   Ten, and cf. Sixty.]
   Six and ten; consisting of six and ten; fifteen and one more.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sixteen \Six"teen`\, n.
   1. The number greater by a unit than fifteen; the sum of ten
      and six; sixteen units or objects.
      [1913 Webster]

   2. A symbol representing sixteen units, as 16, or xvi.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sixteen
    adj 1: being one more than fifteen [syn: sixteen, 16, xvi]
    n 1: the cardinal number that is the sum of fifteen and one
         [syn: sixteen, 16, XVI]