When you are searching for different synonyms of a word, a thesaurus is often of a great help.
The Visual Thesaurus is an interactive tool that allows you to discover the connections between words in a visually captivating display.
http://www.visualthesaurus.com/
Word maps let you search for just the right word and then explore related concepts, revealing the way words and meanings relate to each other. It's a word-lover's delight, with more than 145,000 words and 115,000 meanings organized in an innovative and intuitive design.
Note: you can use it free of charge but you have to reload the free test page if you want to continue to use it without subscription.
Draught of beer, draft beer
- beer served from a tap, beer drawn from a keg
Froth
1. A mass of bubbles in or on a liquid; foam.
2. Salivary foam released as a result of disease or exhaustion.
3. Something unsubstantial or trivial.
4. A fit of resentment or vexation: was in a froth over the long delay.
http://www.thefreedictionary.com/
This dictionary is very comprehensive particularly for complex expressions or idioms and available for free, but in return it is fraught with ads all over the result’s page. It's also interesting to highlight that, in addition to the general dictionary, you have access to specialized vocabulary in medical, legal and financial science along with a very useful dictionary of acronyms.
The dictionary
The Free Dictionary is a very comprehensive dictionary. The main source of The English dictionary is Houghton Mifflin's premier dictionary, the American Heritage® Dictionary of the English Language, Fourth Edition. This authoritative work is the largest of the American Heritage® dictionaries and contains over 200,000 boldface terms and more than 33,000 written examples. The Fourth Edition also incorporates more than 10,000 new words.
Containing 260,000 entries, the general dictionary is augmented with Collins English Dictionary – Complete and Unabridged, and is enhanced by 30,000 illustrations, an audio pronunciation feature, etymologies, abbreviations, biographical entries, and more. Definitions are accompanied by usage examples from classic works of literature.
Pronounciation
Thesaurus
A Thesaurus entry is often linked to a word entry in the dictionary. A picture related to the word semantics is often displayed. 
Translations
Additionally, translations to Spanish, French, German, and Italian are provided by HarperCollins and feature contemporary vocabulary and expressions—including everyday terms
The idioms dictionary
relating to business, computing, current events, tourism and many other topics.
The idioms dictionary is compiled from the Cambridge International Dictionary of Idioms and the Cambridge Dictionary of American Idioms.
