The Collaborative International Dictionary of English v.0.48:

Decimal \Dec"i*mal\, a. [F. d['e]cimal (cf. LL. decimalis), fr.
   L. decimus tenth, fr. decem ten. See Ten, and cf. Dime.]
   Of or pertaining to decimals; numbered or proceeding by tens;
   having a tenfold increase or decrease, each unit being ten
   times the unit next smaller; as, decimal notation; a decimal
   coinage.
   [1913 Webster]

   Decimal arithmetic, the common arithmetic, in which
      numeration proceeds by tens.

   Decimal fraction, a fraction in which the denominator is
      some power of 10, as 2/10, [frac25x100], and is usually
      not expressed, but is signified by a point placed at the
      left hand of the numerator, as .2, .25.

   Decimal point, a dot or full stop at the left of a decimal
      fraction. The figures at the left of the point represent
      units or whole numbers, as 1.05.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Decimal \Dec"i*mal\, n.
   A number expressed in the scale of tens; specifically, and
   almost exclusively, used as synonymous with a decimal
   fraction.
   [1913 Webster]

   Circulating decimal, or Circulatory decimal, a decimal
      fraction in which the same figure, or set of figures, is
      constantly repeated; as, 0.354354354; -- called also
      recurring decimal, repeating decimal, and repetend.
      [1913 Webster]

WordNet (r) 3.0 (2006):

decimal
    adj 1: numbered or proceeding by tens; based on ten; "the
           decimal system" [syn: decimal, denary]
    n 1: a proper fraction whose denominator is a power of 10 [syn:
         decimal fraction, decimal]
    2: a number in the decimal system

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "decimal":
   algorismic, algorithmic, aliquot, cardinal, decagonal, decahedral,
   decasyllabic, decuple, denary, differential, digital, even,
   exponential, figural, figurate, figurative, finite, fractional,
   imaginary, impair, impossible, infinite, integral, irrational,
   logarithmic, logometric, negative, numeral, numerary, numerative,
   numeric, odd, ordinal, pair, positive, possible, prime, radical,
   rational, real, reciprocal, submultiple, surd, tenfold, tenth,
   tithe, transcendental