4(n = noun.quantity) four, foursome, iv, little joe, quadruplet, quartet, quatern, quaternary, quaternion, quaternity, tetrad - the cardinal number that is the sum of three and one;
is a kind of digit, figure
4(s = adj.all) four, iv - being one more than three;
one more than three; denoting a quantity consisting of four items or units; -- representing the number four as an Arabic numeral [WordNet 1.5]
atomic number 4, biosafety level 4, cluster of differentiation 4, july 4, zip + 4