Definition of "effective"

effective

/ɪˈfɛktɪv/

adjective
comparative more effective, superlative most effective
1. Having the power to produce a required effect or effects.
2. Producing a decided or decisive effect.
  Quotations
  Whosoever is an effective, real cause of doing his neighbour wrong, is criminal.
  1651, Jer[emy] Taylor, The Rule and Exercises of Holy Living. […], 2nd edition, London: […] Francis Ashe […]
3. Efficient, serviceable, or operative, available for useful work.
4. Actually in effect.
5. (geometry, of a cycle or divisor) Having no negative coefficients.
6. (physics, for any effective theory) approximate; Not describing the fundamental dynamic changes in some system as they happen.
noun
plural effectives
1. (military) a soldier fit for duty
  Quotations
  The Army of the West reached Corinth sometime after the battle of Shiloh. We were 15,000 effectives, and brought Beauregard's effective force up to 45,000 men.
  1876, Dabney Herndon Maury, Southern Historical Society Papers: Volume 2, Number 4, Recollections of the Elkhorn Campaign