effective

adjective

1 there is no effective treatment for this condition:

successful, effectual, efficacious, productive, constructive, fruitful, functional, potent, powerful;

worthwhile, helpful, of help, of assistance, beneficial, advantageous, valuable, useful, of use.

▷antonyms ineffective; incompetent; weak.

2 a more effective argument can be constructed in support of the opposite point of view:

convincing, compelling, strong, forceful, forcible, powerful, potent, weighty, plausible, efficacious, sound, valid, well founded, telling;

impressive, persuasive, irresistible, credible, influential, conclusive, unanswerable, authoritative;

logical, reasoned, reasonable, well reasoned, rational, lucid, coherent, cogent, eloquent, clear, articulate.

▷antonyms weak.

3 the new law will become effective three months from now:

operative, in force, in effect, in operation, valid, official, signed and sealed;

lawful, legal, licit, legitimate, legally binding, binding;

Law effectual.

▷antonyms invalid.

4 the region did not come under effective Dutch control until 1904:

virtual, practical, essential, operative, actual, implied, implicit, unacknowledged, tacit.

▷antonyms theoretical.

□ be effective

no one doubts that these measures will be effective:

succeed, be successful, work, work out, turn out well, go as planned, have the desired result, get results, be efficacious;

have an effect, take effect, be efficacious, function, act, have results, take hold;

informal come off, pay off, do the trick, do the business;

North American, informal turn the trick.

▷antonyms fail; have no effect.

easily confused words

effective or efficient?

Both these words express approval of the way in which someone or something works; but their meanings are different. Effective describes something which successfully produces an intended result, without reference to morality, economy of effort, or efficient use of resources (the drug is more effective in treating ulcers than its predecessors | the trap was hideously unpleasant and equally hideously effective). Efficient, on the other hand, applies to someone or something able to produce results with the minimum expense or effort, as a result of good organization or good design and making the best use of available resources (staff offer efficient and unobtrusive service).

effective Oxford Dictionary of English