1 successfully producing the result that you want 有效的:
a medicine that is effective against the common cold能治好一般感冒的药物That picture would look more effective on a dark background.那幅画要是用暗色的背景衬托,效果会更佳。 [OPP] ineffective 反义词为 ineffective
2 real or actual, although perhaps not official 真正的,实际上的(也许不是正式的):
The soldiers gained effective control of the town.军队已取得该镇的实际控制权。 ➔effectivenessnoun [U]