diff --git a/go.mod b/go.mod
index e82187e..155e222 100644
--- a/go.mod
+++ b/go.mod
@@ -4,7 +4,7 @@ go 1.21
 
 require (
 	github.com/RoaringBitmap/roaring v1.9.3
-	github.com/blevesearch/bleve_index_api v1.1.12
+	github.com/blevesearch/bleve_index_api v1.2.0
 )
 
 require (
diff --git a/go.sum b/go.sum
index 433da92..9b45c05 100644
--- a/go.sum
+++ b/go.sum
@@ -2,8 +2,8 @@ github.com/RoaringBitmap/roaring v1.9.3 h1:t4EbC5qQwnisr5PrP9nt0IRhRTb9gMUgQF4t4
 github.com/RoaringBitmap/roaring v1.9.3/go.mod h1:6AXUsoIEzDTFFQCe1RbGA6uFONMhvejWj5rqITANK90=
 github.com/bits-and-blooms/bitset v1.12.0 h1:U/q1fAF7xXRhFCrhROzIfffYnu+dlS38vCZtmFVPHmA=
 github.com/bits-and-blooms/bitset v1.12.0/go.mod h1:7hO7Gc7Pp1vODcmWvKMRA9BNmbv6a/7QIWpPxHddWR8=
-github.com/blevesearch/bleve_index_api v1.1.12 h1:P4bw9/G/5rulOF7SJ9l4FsDoo7UFJ+5kexNy1RXfegY=
-github.com/blevesearch/bleve_index_api v1.1.12/go.mod h1:PbcwjIcRmjhGbkS/lJCpfgVSMROV6TRubGGAODaK1W8=
+github.com/blevesearch/bleve_index_api v1.2.0 h1:/DXMMWBwx/UmGKM1xDhTwDoJI5yQrG6rqRWPFcOgUVo=
+github.com/blevesearch/bleve_index_api v1.2.0/go.mod h1:PbcwjIcRmjhGbkS/lJCpfgVSMROV6TRubGGAODaK1W8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
diff --git a/segment.go b/segment.go
index 8e4a3d9..a6d1183 100644
--- a/segment.go
+++ b/segment.go
@@ -178,3 +178,59 @@ type FieldStats interface {
 	Aggregate(stats FieldStats)
 	Fetch() map[string]map[string]uint64
 }
+
+// ThesaurusSegment provides access to a thesaurus within a specific segment of the index.
+type ThesaurusSegment interface {
+	Segment
+	// Thesaurus returns the Thesaurus with the specified name.
+	Thesaurus(name string) (Thesaurus, error)
+}
+
+// Thesaurus encapsulates a structured collection of terms and their associated synonyms.
+type Thesaurus interface {
+	// SynonymsList retrieves a list of synonyms for the specified term. The `except` parameter
+	// excludes specific synonyms, such as those originating from deleted documents. The `prealloc`
+	// parameter allows the use of preallocated memory to optimize performance.
+	SynonymsList(term []byte, except *roaring.Bitmap, prealloc SynonymsList) (SynonymsList, error)
+
+	// AutomatonIterator creates an iterator over the thesaurus keys/terms using the provided automaton.
+	// The iteration is constrained by the specified key range [startKeyInclusive, endKeyExclusive).
+	// These terms or keys are the ones that have a SynonymsList associated with them, in the thesaurus.
+	AutomatonIterator(a Automaton, startKeyInclusive, endKeyExclusive []byte) ThesaurusIterator
+
+	// Contains checks if the given key exists in the thesaurus.
+	Contains(key []byte) (bool, error)
+}
+
+// ThesaurusIterator iterates over terms in a thesaurus.
+type ThesaurusIterator interface {
+	// Next returns the next entry in the thesaurus or an error if iteration fails.
+	Next() (*index.ThesaurusEntry, error)
+}
+
+// SynonymsList represents a list of synonyms for a term.
+type SynonymsList interface {
+	// Iterator returns an iterator to traverse the list of synonyms.
+	// The `prealloc` parameter can be used to reuse existing memory for the iterator.
+	Iterator(prealloc SynonymsIterator) SynonymsIterator
+
+	Size() int
+}
+
+// SynonymsIterator provides a mechanism to iterate over a list of synonyms.
+type SynonymsIterator interface {
+	// Next returns the next synonym in the list or an error if iteration fails.
+	Next() (Synonym, error)
+
+	Size() int
+}
+
+// Synonym represents a single synonym for a term in the thesaurus.
+type Synonym interface {
+	// Number returns the document number from which the synonym originates.
+	Number() uint32
+	// Term returns the textual representation of the synonym.
+	Term() string
+
+	Size() int
+}