Merriam-Webster Collegiate Dictionary - active

 adjective  Etymology: Middle English, from Anglo-French or Latin; Anglo-French actif, from Latin activus, from actus, past participle of agere to drive, do — more at agent  Date: 14th century  1. characterized by action rather than by contemplation or speculation an ~ life  2. producing or involving action or movement  3.  a. of a verb form or voice asserting that the person or thing represented by the grammatical subject performs the action represented by the verb hits in “he hits the ball” is ~  b. expressing action as distinct from mere existence or state  4. quick in physical movement ; lively  5. marked by vigorous activity ; busy the stock market was ~  6. requiring vigorous action or exertion ~ sports  7. having practical operation or results ; effective an ~ law  8.  a. disposed to action ; energetic took an ~ interest  b. engaged in an action or activity an ~ club member  c. of a volcano currently erupting or likely to erupt — compare dormant 2a, extinct 1b  d. characterized by emission of large amounts of electromagnetic energy an ~ galactic nucleus  9. engaged in full-time service especially in the armed forces ~ duty  10. marked by present operation, transaction, movement, or use an ~ account  11.  a. capable of acting or reacting ; reacting readily ~ nitrogen ~ ingredients  b. tending to progress or to cause degeneration ~ tuberculosis  c. of an electronic circuit element capable of controlling voltages or currents  d.  (1) requiring the expenditure of energy ~ calcium ion uptake  (2) functioning by the emission of radiant energy or sound radar is an ~ sensor  12. still eligible to win the pot in poker  13. moving down the line ; visiting in the set — used of couples in contredanses or square dances  • ~ noun  • ~ly adverb  • ~ness noun