Echo
Reverberation, Influence, Repercussion, Reaction
noun, verbal noun
An anti echo is still an echo! It's just going back and forth with a normal echo. Together they get a weird reverberation going.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
この記事への反響はとても大きかった。
The reaction towards this article was huge.