Documentation can be found following the link below:
https://api.stackexchange.com/docs/synonyms-by-tags
public override IBridgeResponseCollection<TagSynonym> GetTagsSynonyms(string[] tags, TagSynonymsQuery parameters = null) { return GetApiResultCollection<TagSynonym, TagSynonymsQuery>(ApiMethodEnum.SynonymsByTags, CreateTagsVector(tags), parameters); }