add_filter( 'pre_comment_content', 'wps_filter_comment' );
function wps_filter_comment($comment) {
$replace = array(
// 'WORD TO REPLACE' => 'REPLACE WORD WITH THIS'
'foobar' => '*****',
'hate' => 'love',
'zoom' => '<a href="http://zoom.com">zoom</a>'
);
$comment = str_replace(array_keys($replace), $replace, $comment);
return $comment;
}