Eva Word Lookup – not listed under the extensions, but run against Wordnet, the lexical database for English – enables you to study your English words in depth. This lookup gives you information organized by the following aspects of your word, linked from an overview of each word type your search term can belong to:
the coordinate terms (sisters)
the derived forms
the synonyms/hypernyms (ordered by estimated frequency)
the hyponyms (troponyms for verbs)
the holonyms, for nouns
the meronyms, for nouns
sample sentences, for verbs
Below is what results look like for example search term “design”: