Order by the last word of the string

orderby-last-word.php

/**
 * Order by last word in title.
 *
 * @param string $orderby orderby
 * @param object $query data
 *
 * @link https://wordpress.stackexchange.com/questions/1003/order-posts-by-last-word-in-title
 *
 * @return string
 */
function elpuas_orderby_last_word( $orderby, $query ) {
    global $wpdb;
    if ( 'elpuas_last_word' === $query->get( 'orderby' ) ) {
        $orderby = "SUBSTRING_INDEX({$wpdb->posts}.post_title, ' ', -1)";
    }
    return $orderby;
}

add_filter( 'posts_orderby', 'elpuas_orderby_last_word', PHP_INT_MAX, 2 );