Finding id of taxonomy by name in custom post type

@Gil, your solution in comment seems to be excellent!
I just modified a small part to be sure not to have a PHP warning on execution.

$w_year = $_GET['w_year'];

$catid = '';
$taxonomies = get_taxonomies();
foreach ( $taxonomies as $taxonomy ) { 
    if ( $term_object = get_term_by( 'slug', $w_year , $taxonomy ) ) {
        if ( !empty($term_object->term_id) ) {
            $catid = $term_object->term_id; 
            break; 
        }
    } 
}