Ok. So thankyou world for not helping. If anyone comes across this post, here’s how you can solve the problem.
I placed the following code at THE START of my .htaccess file, before any wordpress .htaccess code.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_URI} ^/subdirectory/(.*)$ [OR]
RewriteRule ^.*$ - [L]
</IfModule>
If you are greeted with a generic 404 page instead of your site’s 404 error page, the code IS WORKING. Your subdirectory’s location is not in the right place. Investigate your folder structure and make sure the subdirectory you want to get to is placed in the public_html folder (your site root).