Syntax: choose from drop-down list
This allows you to select a level of equivalence matching. You can limit results to specific matches, or you can allow synonyms and phrases. The values are described as follows:
Disabled: no phrase recognition and no synonyms
(equivalences). Only searches for the the actual terms in a
query. This is regardless of
Phrase recognition only: recognize query word groups that are
known phrases and search for them as phrases.
Phrases & Allow synonyms: phrase recognition plus allows the
tilde ( ) operator to match synonyms on specific query terms
Phrases & Use synonyms by default: phrase recognition and
matching synonyms on all query terms (tilde to turn off on specific
Using the Thesaurus (section 5.3).