Learner's definition of EFFECTIVE
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.
2 of a law, rule, etc. : in use : active 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