This might seem like a no-brainer, but there seems to be some misunderstanding about the function or purpose of a dictionary, particularly on social media. 

A good dictonary serves a number of functions:

• Dictionaries record language as it is used. Words are added to a dictionary when they become frequently used by the people who speak the language. One can’t just make up a word and apply to have it included. It needs to become part of the commonly spoken language of the people first. 
  
• Dictionaries give meanings of words. 
  
• Dictionaries provide accepted spellings of words, and often include alternative spellings. This varies according to the country of publication, particularly when it comes to the differences between English and American spellings of words. 
  
• Dictionaries often give advice as to how a word should be pronounced. This too will vary according to common usage in the country in which the dictionary is published. Some dictionaries use the regular alphabet to achieve a phonetic respelling, while others use the International Phonetic Alphabet. 

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• Online dictionaries do all that, and also offer voice recordings to demonstrate pronunciation. They also provide direct links to thesaurus entries and related words. 
  
• Dictionaries can also settle arguments. They are helpful in adjudicating spelling games such as Scrabble, and settling arguments about how a word is spelt or what it means. 

There are, however, things that dictionaries neither seek nor claim to do. 

• A dictionary is not a rule book for the language. Just because a word isn’t in the dictionary does not actually mean that it’s not a word. If people say it, and other people understand it when they do, it’s a word. 
  
• An Australian dictionary is not useful for recording American English, and vice versa.
  
• A dictionary generally doesn’t give the etymology of a word, although it might suggest that it’s an old, obsolete or archaic word.
  There are etymological dictionaries that do this, but they are far less popular than the regular kind of dictionary with which most people are familiar. Some etymological dictionaries are specific to a particular area of study, while the Online Etymological Dictionary is a vast resource of the history of a plethora of English words and phrases.
  
• A dictionary generally won’t include words that have fallen out of use. In the large dictionary on my desk at home, words like ‘forswunk’ and ’trustful’ are no longer included, while they would have been many years ago. It doesn’t mean they are no longer words: it simply means the likelihood of someone wanting to look them up is considered far less than someone wanting to look up ‘exhausted’ or ‘melancholy’ instead. 

What’s the best dictionary to use? 

Most people will find the greatest value in a dictionary which is compiled, written and published in the country in which they live and work. Most people will want one that is up to date. 

For Australian English, I love the Macquarie Dictionary.
For UK English, there is nothing that surpasses the Oxford English Dictionary, but the Cambridge English Dictionary is very good, too.

I have no preferred dictionary for American English, because I don’t use one. (If you can make a recommendation, please leave a comment!)

Old dictionaries hold particular appeal for scholars, teachers and lovers of language. They can be invaluable resources for authors and readers, too.