Bookkeeper is the word in the English language with the most pairs of letters adjacent to each other, aside from the highly related word bookkeeping, which has the exact same number of pairs.

Bookkeeper, that's 3 pairs.
 |/|/|/
 1 2 3

As interesting as this is, maybe there should be a nodes that don't matter metanode.

Book"keep`er (?), n.

One who keeps accounts; one who has the charge of keeping the books and accounts in an office.

 

© Webster 1913.