You could use a regular expression for this. Depends if you want to find all instances of the word.
http://php.net/manual/en/function.preg-match.php
or
http://www.php.net/manual/en/function.preg-match-all.php to find all instances instead of just 1 match.
Also if you want to search all of them at the same time you can do that as well.
Something like
\bis\b should work. this should search for the actual word "is", so tis would not match, but your case "is," will even with that comma there.
to search for any of them at the same time you can do
\b(is|This|big)\b this will match is and This, but big won't be found.
Update
I'm not exactly sure what you want 100%, but you can just add the comma. IE: "/\b(copenhagen|kobenhavn)\b,/i" now if you want to include the comma in the search you can do, "/\b(copenhagen|kobenhavn)\b,?/i", so the comma is optional. If you did
\b(copenhagen|kobenhavn|denmark)\b,?
on
"Copenhagen, Denmark"
it will match
Copenhagen,
and
Denmark
Note the comma in Copenhagen, but the comma is optional in this case. So it will match the word with or without it.