effective

Etymology

From French effectif, from Latin effectīvus (“productive; effective”), from efficiō (“I make; I bring about”).

adj

1. Having the power to produce a required effect or effects.
   The pill is an effective method of birth control.
2. Producing a decided or decisive effect.
   The president delivered an effective speech!
3. Efficient, serviceable, or operative, available for useful work.
   How long does it take to make a bunch of civilians an effective military force?
   My effective income after taxes and child support is $500 a month.
   The effective radiated power is determined by multiplying the transmitter power output with the antenna gain.
   The effective voltage of an alternating current is 0.7 times its peak voltage.
4. Actually in effect.
   The curfew is effective at midnight.
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

1. (military) a soldier fit for duty
   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