in reply to hash array

%dictionary is a hash. You are passing it as a hash reference argument to readWords() and sortDictionary(), via \%dictionary. So far so good.

Now, inside the functions readWords() and sortDictionary(), you need to consume the argument you passed in. But your code currently does not do that. (Instead, it is consuming the closed-over lexical my %dictionary - if you don't understand this last sentence, ignore it for now).

Let change your functions to consume the passed in hashref. To avoid confusion, I renamed the variable inside the functions to be $dict instead. Here's the same code with modifications indicated:
my %dictionary;

readWords(\%dictionary);
sortDictionary(\%dictionary);

sub readWords {
   my ($dict) = @_; # <<--- grab hashref argument 

   $numWords = 0;

   open FILE, $ARGV[0] or die $!;

   while (my $lines = <FILE>) {
      $numWords++;
      chomp $lines;

      my ($words, $definitions) = split('/', $lines);
      $words = lc($words);
      $dict->{$words} = $definitions; # <<--- renamed $dictionary to $
+dict
   }
   foreach $key (%{ $dict }) {  # <<--- use $dict exclusively, but as 
+the hash it's pointing to
      print $dict->{$words}; # <<--- renamed $dictionary to $dict
      print $result . "\n";
   }
   close FILE;
}

sub sortDictionary {
   my ($dict) = @_; # <<--- grab hashref argument 

   foreach my $key (sort keys %{ $dict }) {  # <<--- use $dict exclusi
+vely, but as the hash it's pointing to
      $key =~ /^(.)/;
      my $line = $key . '/' . $dict->{$key} . "\n"; # <<--- renamed $d
+ictionary to $dict
      print $line;
   }

}

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