See the dictfmt man:
--index-keep-orig
When --utf-8 is specified headwords are lowercased and non-
alphanumeric characters are removed from it before saving to
.index file in order to simplify the search. When
--index-keep-orig option is used fourth column is created (if
necessary) in .index file, and contains an original headword
which is returned by MATCH command. This option may be useful
to prevent converting " AT&T" to " ATT" or to keep proper nouns
with uppercased first letter.