dictionary.cambridge.org
www.definitions.net
www.urbandictionary.com
The most upvoted single word on Urban Dictionary is www.urbandictionary.com/define.php?term=sex for obvious reasons.
www.reddit.comwww.wordreference.com
en.wiktionary.org
www.urbandictionary.com
www.merriam-webster.com
www.definder.net
www.vocabulary.com