Reverse Dictionary - Describe a concept and get back a list of words

ManyThings.org - ManyThings is a multiplatform and user friendly application for students of ESL or EFL to learn the meanings and definitions of different terms and phrases.

Writefull Thesaurus - A Google Docs add-on that uses AI to give you synonyms

Wordspy.com - Finding the meaning of a new word or the word that is not being used on the international level is surely a way of conjuring its existence.

Dictionary Anywhere - Dictionary Anywhere is an open-source and easy-to-use browser extension for Mozilla Firefox and Google Chrome that allows you to check definitions easily while browsing the web.

DAREDictionary.com - Dictionary of American Regional English presents the meaning of words region wise.