How can I check if a taxonomy has more than one item?

And if you want to check if current post has more than one term in given taxonomy (it’s not very clear in your question and this version makes much more sense for me…), then function get_the_terms will come handy:

$terms = get_the_terms( $post, $taxonomy );
echo ( count($terms) > 1 ) ? 'Destinations' : 'Destination';