a.  1.  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;
 
n.  1.  A number expressed in the scale of tens; specifically, and almost exclusively, used as synonymous with a decimal fraction.

Noun  1.  decimal  a proper fraction whose denominator is a power of 10 Synonyms: decimal fraction 
2.  decimal  a number in the decimal system  
Adj.  1.  decimal  numbered or proceeding by tens; based on ten; "the decimal system" Synonyms: denary 
2.  decimal  divided by tens or hundreds; "a decimal fraction"; "decimal coinage" 