the codex has exacly what you need: get_page_by_title()
Example
$page = get_page_by_title( 'About' );
$the_excerpt = $page->post_excerpt;
or
$page = get_page_by_path( 'parent-page/sub-page' );
the codex has exacly what you need: get_page_by_title()
$page = get_page_by_title( 'About' );
$the_excerpt = $page->post_excerpt;
or
$page = get_page_by_path( 'parent-page/sub-page' );