noun

1. That which is permanent or invariable.

2. A quantity that remains at a fixed value throughout a given discussion.

3. Any property of an experiment, determined numerically, that does not change under given circumstances.

adjective

1. Unchanged through time or space; permanent.

2. Consistently recurring over time; persistent.

3. Steady in purpose, action, feeling, etc.

Synonyms: nonchanging, unaltering, unvarying