Definition of effective adjective from the Oxford Advanced Learner's Dictionary

Oxford3000

effective

adjective
ɪˈfektɪv
 
; ɪˈfektɪv
 
 
1 producing the result that is wanted or intended; producing a successful resultLong prison sentences can be a very effective deterrent for offenders.Aspirin is a simple but highly effective treatment.drugs that are effective against cancerSome people believe that violence is an effective way of protesting.I admire the effective use of colour in her paintings.
Opposite
ineffective
see also cost-effective
2 [only before noun] in reality, although not officially intendedthe effective, if not the actual, leader of the partyIn spite of what they are told, parents have no effective choice of schools.He has now taken effective control of the country.3 (formal) (of laws and rules) coming into useThe new speed limit on this road becomes effective from 1 June.effectiveness (also less frequent effectivity
ɪˌfekˈtɪvɪti
 
; ɪˌfekˈtɪvɪti
 
)
noun [uncountable]to check the effectiveness of the security system