ef·fec·tive 
/ɪˈfɛktɪv/ adjective
/ɪˈfɛktɪv/ adjective 1 [more effective; most effective] : producing a result that is wanted : having an intended effect
▪ drugs effective in the treatment of a disease = drugs effective in treating a disease = drugs effective against a disease ▪ It's a simple but effective technique. ▪ He gave an effective speech. — opposite ineffective 2 of a law, rule, etc. : in use : active
▪ The law becomes effective [=the law takes effect; the law will start to be used] next year. ▪ the effective date of the law [=the day when the law starts to be used] 3 : starting at a particular time — used to introduce a clause ▪ Effective [=starting, as of] tomorrow, the store will be open until 8:00 p.m. every day. ▪ Effective next month, the landfill will no longer accept old televisions. 4 always used before a noun — used to describe something that exists or has an effect but that is not officially stated or recognized ▪ the effective tax rate ▪ The army has taken effective control of the city.
▪ drugs effective in the treatment of a disease = drugs effective in treating a disease = drugs effective against a disease ▪ It's a simple but effective technique. ▪ He gave an effective speech. — opposite ineffective
▪ The law becomes effective [=the law takes effect; the law will start to be used] next year. ▪ the effective date of the law [=the day when the law starts to be used]
— ef·fec·tive·ness noun [noncount]
▪ The effectiveness of the drug was questioned.
▪ The effectiveness of the drug was questioned.
