Score 8
The highest-scoring word in the Wolfram dictionary is:
interrelatedness
Which consists of:
INTERRElateDness
and
interreLATEdNESS
Found using:
n = 8;
wl = ToLowerCase@DictionaryLookup[Repeated[_, {n}]];
wl2 = ToLowerCase@DictionaryLookup[Repeated[_, {2 n}]];
subwords =
Cases[Table[
w -> Select[wl,
LongestCommonSequence[w, #] == # &&
LongestCommonSubsequence[w, #] != # &], {w, wl2}],
Pattern[p, _ -> {_, __}]];
Cases[subwords, (w_ -> {___, a_, ___, b_, ___}) /; (Sort[
Characters[w]] == Sort[Characters[a]~Join~Characters[b]]) :> {w,
a, b}]