my $words = {
  'foo' => {
    nn => 1,
    nns => 1,
  },
  'bar' => {
    nvbg => 1,
    np => 1,
  },
};

my $lookup = 'foo';
my $tag = 'nn';
print $words->{$lookup}->{$tag}; # Would print '1'
foreach my $tag (keys %{$words->{$lookup}}) {
  # This would print all the tags for a specified word, in no particular order
  print $tag . "\n";
}
# To add a new word and/or tag:
$words->{'baz'}->{'nps'} = 1;
# To delete a tag:
delete $words->{'baz'}->{'nps'};
# To check for a specific tag:
if ( $words->{'baz'}->{'nps'} ) { ... }