$ cat ./generate_words.pl
#!/bin/env perl
use strict;
my $numofwords= 50_000_000;
for (my $i=0; $i<$numofwords; ++$i)
{
        my @chars = ( "A" .. "Z", "a" .. "z", 0 .. 9, qw(! @ $ % ^ & *) );
        my $rin = join("", @chars[ map { rand @chars } ( 1 .. 5 ) ] ) ;
        print $rin, "\n";
}

##</code><code>##

$ time perl ./generate_words.pl > words.txt;

real    7m54.686s

$ time ( < words.txt psql -d test -c "
   drop table if exists words;
   create table words (word text, id serial);
   copy words(word) from stdin csv; " )

real    1m16.223s