That code is broken regardless of whether it's in a module or a stand-alone script. The problem lying at

  foreach (@words) { my $some_words{$_} = "1"; }
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The problem is that you're trying to declare a lexical element of the hash %some_words, which, firstly, hasn't been declared (not necessarily a problem, but still something to be concerned with) and secondly is illegal (as perl only has lexical variables, not lexical hash elements (but dynamic hash elements are possible with local, but that doesn't apply in this case)).

What you want is to declare the hash and have it exported e.g

  @EXPORT = qw/ loadwords %somewords /;

  use vars '%somewords';

  ## in the loadwords function

  for(@words) { $somewords{$_} = "1"; }
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This is sort of hash initialisation is more idiomatically done with a single map statement e.g

  %somewords = map { $_ => 1 } @words;
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For more information on exporting and modules see. Exporter and perlmod.