ef‧fec‧tive S2 W1
successful, and working in the way that was intended [≠ ineffective]:
The cheaper drugs are just as effective in treating arthritis.
the painting's highly effective use of colour
Training is often much less effective than expected.
the most effective ways of reducing inner city congestion
2 [no comparative, not before noun]SCL
if a law, agreement, or system becomes effective, it officially starts
The cut in interest rates is effective from Monday.
3 [no comparative, only before noun]
real rather than what is officially intended or generally believed:
The rebels are in effective control of the city.
—effectiveness noun [uncountable]