engaged in action; characterized by energetic work, participation, etc.; busy

an active life.

being in a state of existence, progress, or motion

active hostilities.

involving physical effort and action

active sports.

having the power of quick motion; nimble

active as a gazelle.

characterized by action, motion, volume, use, participation, etc.

an active market in wheat; an active list of subscribers.

causing activity or change; capable of exerting influence ( opposed to passive )

active treason.

effective ( opposed to inert )

active ingredients.

Grammar . noting or pertaining to a voice of verbal inflection in which typically the subject of the sentence is represented as performing the action expressed by the verb ( opposed to passive )

Writes in He writes a letter every day is an active verb form.

requiring or giving rise to action; practical

an active course.

(of a volcano) in eruption.

Accounting . profitable; busy

active accounts.

requiring personal effort or attention; not automatic

an active alarm system.

interest-bearing

active paper.

Medicine/Medical . acting quickly; producing immediate effects

active remedies.

Sociology . (of a crowd) engaging in purposeful activity, often of a militant nature. Compare expressive ( def. 4 ) .

Aerospace . able to transmit signals

an active communications satellite.

Electronics . (of a device or system) acting as a source of electrical energy, as a generator, or capable of amplifying or converting voltages or currents, as a transistor or diode.

(of a solar heating system) accumulating and distributing solar heat by mechanical means.

Military . serving on active duty.

Grammar .

the active voice.

a form or construction in the active voice.

an active person, member, subscriber, etc.

The circular was mailed only to the actives on our list.

Informal . something showing considerable action or activity

On the stock market there was heavy trading in the actives.

adjective

abeyant , dormant , immobile , inactive , inert , lazy , sluggish , disinterested , idle , indifferent , quiescent , quiet , latent , passive , sedentary

adjective

alive , astir , at work , bustling , effective , efficacious , exertive , flowing , functioning , going , hasty , impelling , in force , in play , in process , mobile , movable , moving , operating , operative , progressive , pushing , rapid , restless , rolling , running , rushing , rustling , shifting , simmering , speeding , speedy , streaming , swarming , traveling , turning , walking , workingnotes:active knowledge is the knowledge of a language which a user actively employs in speech or writing , as opposed to passive knowledge , which is what a person understands in what he/she hears or reads , aggressive , agile , alert , animated , assiduous , bold , brisk , busy , chipper , daring , dashing , determined , dexterous , diligent , dynamic , eager , energetic , engaged , enlivened , enterprising , enthusiastic , eventful , fireball , forceful , forcible , fresh , frisky , hard-working , high-spirited , hyper , industrious , intense , inventive , jumping , keen , lively , nimble , on the move , perky , persevering , purposeful , quick , ready , resolute , sharp , sprightly , spry , whiz * , zealousnotes:active knowledge is the knowledge of a language which a user actively employs in speech or writing , working , driving , dynamical , peppy , zippy , kinetic , strenuous , vigorous , athletic , awake , doer , drastic , employed , engage , engrossed , expeditious , flourishing , goer , hardworking , impetuous , indefatigable , intent , operose , sedulous , spirited , sprite , transitive , vigilant , vivacious