1.a quantity that does not vary
2.a number representing a quantity assumed to have a fixed value in a specified mathematical context;
the velocity of light is a constant
3.persistent in occurrence and unvarying in nature;
maintained a constant temperature
4.continually recurring or continuing without interruption;
constant repetition of the exercise
5.steadfast in purpose or devotion or affection;
a man constant in adherence to his ideals
6.uninterrupted in time and indefinitely long continuing;
the ceaseless thunder of surf