my @words = get_words_to_check();

my %hash = map { $_ => 1 } @words;

while (my $line = <>)
{
  chomp $line; 
  delete $hash{$line} if exists $hash{$line}; # The if exists isn't required here, but it does make it look cleaner
}

my @good_words = grep { exists $hash{$_} } @words; # Keep the original order
my @good_words_2 = keys %hash; # Don't care about the original order