communicate new/changed values between taxonomies
Unfortunately you are probably stuck writing your own module. You need to implement hook_taxonomy_term_update and hook_taxonomy_term_insert.  In each you can check the item being updated and force a change on any associated terms in the other taxonomy.

The one thing to be careful of is an update spiral. Forcing an update on associated terms will then force an update of the original term, because it is now associated.  Because the changes in those two hooks are not committed to the db until the whole mess resolves it will lock up unless you put in a variable to keep it from spiraling.

For example:

if ($term-&gt;tid == args(2)) _update_related_terms($term);


should check the term being updated against the current page.  If they do not match it won't fire. (I haven't tested this snippet, so test thoroughly!)

Then in _update_related_terms

function _update_related_terms($term){
  $associated_terms = $term-&gt;associated_term_field; 
  if (isset($associated_terms['und'][0]['tid']) &amp;&amp; $associated_terms['und'][0]['tid'] != ''){
    foreach ($associated_terms['und'] as $key =&gt; $value){
      if (isset($value['tid']) &amp;&amp; $value['tid'] != ''){
        //check the associated term here.  You could load it, or check the db, or all sort of things
      }
    }
  }
}


I know I am using und in this example, but it is off the cuff.  Again, not tested

Please note: this example is for d7.