We are currently using the below .htaccess code to redirect /artist/* to /artists/* which works well however, we need the URL /artist/ to remain available and not redirect through to /artists/ is this possible with .htaccess? We'd like to avoid a PHP based redirect if possible.
RewriteRule ^artist/(.*)$ /artists/$1 [R=301,NC,L]
If you don't want to change URL in your browser means you don't want to redirect and only want to rewrite to different URL then try following(we need to remove R flag from rules. Also this rule considers that you have /artists in your root directory if that's not the case then remove its starting slash in Rule.
RewriteRule ^artist/(.*)/?$ /artists/$1 [NC,L]