The most common linguistic settings when search are suffix processing, and thesaurus use. When suffix processing is enabled suffixes from the suffix list are removed as long as the resulting word is at least minwordlen characters long. After that by default trailing vowels and repeated consonants are removed. This last removal can be disabled with the defsuffrm flag.

There are two possible uses for the thesaurus. With the thesaurus set, but keepeqvs disabled the thesaurus is used to find phrases in the query automatically. With keepeqvs enabled a set of words and phrases is generated to match the query term. If any of them is found, that term is considered to have matched.

To enhance searches you can customize the thesaurus. This can be either a replacement of the thesaurus, or modifications to the provided thesaurus. The default thesaurus is large, and may have too many entries for a niche application, in which case you could replace the thesaurus, otherwise you can edit the thesaurus.

For small edits to the thesaurus you can use the backref in interactive mode, otherwise you can create a file, and have backref compile it in batch mode.