effective

Something that works well and gives the result you want.

• This is an effective treatment for headaches.
• Their new strategy was surprisingly effective.
• Which method is most effective for teaching beginners?

How to use it: effective against something (This spray is effective against mosquitoes.); effective in doing something (The lessons were effective in improving her reading.)

Similar words: successful, useful, efficient

Opposites: ineffective

Common phrases: effective treatment, effective method, effective against something, effective protection

Officially applying or operating from a particular time.

• The new rules are effective immediately.
• The agreement became effective last month.
• What is the effective date of the change?

How to use it: effective from a date (The contract is effective from the first of June.); effective on a date (The new policy becomes effective on Monday.)

Similar words: in force, valid

Common phrases: effective date, become effective, effective from monday

Having a strong effect on how people feel, think, or act.

• Her speech was brief but effective.
• The silence made the final scene especially effective.
• He delivered an effective argument that changed several minds.

Similar words: powerful, persuasive, forceful

Opposites: ineffective

Common phrases: effective speech, effective ending, effective argument

Actually present or held in practice, even without official recognition.

• The rebels had effective control of the town.
• She held effective power despite having no official title.
• The agreement gave workers effective control over hiring.

Similar words: actual, de facto

Common phrases: effective control, effective command, effective power

Starting officially at the time mentioned.

• Effective Monday, parking will be free.
• The company raised its prices effective yesterday.
• Effective next year, all students will receive free lunches.

How to use it: effective + time (Effective tomorrow, the office will open at eight.)

Similar words: as of, starting from

Common phrases: effective immediately, effective tomorrow, effective next month