Don't know about faster, but I think this is more elegant: 
++$$ngram{$_} for grep defined,
  "_${word}_" =~ /(?=(((((.).).).).))|(?=((((.).).).))|
                  (?=(((.).).))|(?=((.).))|(?=(.))/gx;

[download]
 Update: Perhaps I had better say, dog slow, but pretty. Thanks for the benchmark, Abigail. This version adds .'s to avoid MINMATCH and is only slightly faster. 
$ngram_y2 = {};
for my $word (@large_wordlist) {
  ++ $$ngram_y2 {$_} for grep defined,
  "_${word}_" =~ / (?=(((((.).).).).)).
                |    (?=((((.).).).)) .
                |     (?=(((.).).))   .
                |      (?=((.).))     .
                |       (?=(.))       ./gx;
}

[download]

In reply to Re: Fasten up NGram generation code? by ysth
in thread Fasten up NGram generation code? by PetaMem

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