Merriam-Webster Collegiate Dictionary - constant

 I. adjective  Etymology: Middle English, from Middle French, from Latin ~-, constans, from present participle of constare to stand firm, be consistent, from com- + stare to stand — more at stand  Date: 14th century  1. marked by firm steadfast resolution or faithfulness ; exhibiting constancy of mind or attachment a ~ friend  2. invariable, uniform a ~ flow  3. continually occurring or recurring ; regular a ~ annoyance  Synonyms: see faithful, continual  • ~ly adverb  II. noun  Date: 1832 something invariable or unchanging: as  a. a number that has a fixed value in a given situation or universally or that is characteristic of some substance or instrument  b. a number that is assumed not to change value in a given mathematical discussion  c. a term in logic with a fixed designation