constant (kon"stent) 

adj.

1. steady in purpose: resolute; persevering; faithful

2. Steady i movement.

3. Long-continuing, or continually recurring.

4. Invariable

5. Firm; positive; consistent

noun

1. That which is permanent or invariable.

2. Mathematics: A quantity which retains a fixed value throughout a given discussion.

3. Science       : Any characteristic of a substance, event, or phenomenon,, numerically determined, that remains always the same under specified conditions, as gravitation, the velocity of light, the melting or freezing point, etc.

Source: Funk & Wagnalls