adjective

1. not changing; remaining the same; specif.,
   1. remaining firm in purpose; resolute
   2. remaining steady in affections or loyalties; faithful
   3. remaining free from variation or change; regular; stable
2. going on all the time; continual; persistent constant interruptions

Etymology: ME & OFr constaunt < L constans: see constancy

noun

1. anything that does not change or vary
2. Math., Physics
   1. a quantity that always has the same value
      in full absolute constant
   2. a quantity, vector, etc. assumed to have one value throughout a particular discussion or investigation
      in full arbitrary constant