You can change the
/search/ part to something else, like
/topic/, but it will be harder to remove it completely, since that will conflict with WordPress Pages (is
/banana/ a Page with the title "Banana" or is it the result page for the search term "Banana"?).
To change the part, hook into the
init action and change the
add_action( 'init', 'wpse21549_init' );
$GLOBALS['wp_rewrite']->search_base = 'topic';
You will need to place this snippet of code in your theme's
function.php file, or in a new file that you create and that you place in the
/wp-content/plugins/ directory. After you did this, visit the Permalinks setting page to flush the rewrite rules.
However, by default when you submit a search you will end up on a URL like
?s=Banana. There are plugins that change this (Ramukar linked to one, but it has the
/search/ part hardcoded and has other issues), and Hudson Atwell linked to a simple approach (even too complicated now: you don't need to add the rewrite rule to Apache, as WordPress already contained them since version 1.5).