A few extras / tweaks for the WordPress plugin Glossary by Codeat: https://wordpress.org/plugins/glossary-by-codeat/

shortcodes.php

<?php
/**
 * You can add this code inside your (child) theme's `functions.php` 
 * or within a PHP-file inside your `mu-plugins` folder
**/


/**
 * Adds the shortcode [glossary-total]
 *
 * @returns the total number of published glossary items
 **/
add_shortcode( 'glossary-total', function() {
	return wp_count_posts('glossary')->publish;
});

single-glossary.php

<?php
/**
 * You can add this code inside your (child) theme's `functions.php` 
 * or within a PHP-file inside your `mu-plugins` folder
**/


/**
 * Filter to add the additional glossary terms beneath the singular glossary content
 *
 * @var (string) $the_content
 * 
 * @returns (string) $the_content
**/
add_filter('the_content', function( $the_content ) {

    /** 
     * Make sure we're on a singular glossary page and we're not inside the WordPress Dashboard
    **/
  	if ( is_singular('glossary') && ! is_admin() )
    {
        /** Get all additional terms (the contents of the 'glossary_tag' post meta field) **/
      	$additional_terms = get_post_meta( get_the_ID(), 'glossary_tag', true );

      	$synonyms = [];
        
        /** Add the main term to the 'additional terms' (as first in the array $synonyms) **/
      	$synonyms[] = sprintf( '<span class="glossary-additional-term">%s</span>', get_the_title() );
      
        /** Make sure we have additional terms before we're going to loop through them **/
      	if ( '' != $additional_terms && null != $additional_terms )
        {
            /**
             * Loop through the additional terms
             *
             * Whitespace before & after each (comma-separated) additional term is removed
            **/ 
          	foreach ( explode( ',', $additional_terms ) as $additional_term )
              	$synonyms[] = sprintf( '<span class="glossary-additional-term">%s</span>', trim( $additional_term, " ") );
        }
      
        /**
         * Add a spacer widget (height: 5px) and then the additional terms inside a p-element to $the_content
         *
        **/
        $the_content .= sprintf( '<div class="ct-widget widget widget_block">
<div style="height:5px" aria-hidden="true" class="wp-block-spacer"></div>
</div><p class="glossary-tags has-small-font-size">%s</p>', implode( ' ', $synonyms ) );

    }
  
    /**
     * Return the contents of $the_content
     *
     * Omitting this would mean nothing will be displayed, on all posts/pages/etc!
    **/
  	return $the_content;

}, 1, 9998);