cheers, mate!

Today's lesson brought to mind some of the different ways some words are primed for those English-users living in the UK (where I was on exchange). One example is the salutation, 'cheers'. In the Singaporean context, 'cheers' is used when toasting drinks as a way of wishing fellow drinkers good health and joy. You can imagine my surprise when I heard a hostel-mate say 'cheers' to me when I held the door open for him, or when I waved goodbye to a classmate.
I decided to check out the various dictionaries to discover if 'cheers' could be found with the observed usage attributed to it.
The Oxford English Dictionary was the natural first choice as I had observed its usage most widely in the UK. However, the word was non-existent!
On the contrary, the Oxford Advanced Learners Dictionary possessed the term with all three meanings recorded. (http://www.oup.com/oald-bin/web_getald7index1a.pl)
cheers /tz; NAmE trz/ exclamation

1 a word that people say to each other as they lift up their glasses to drink
2 (BrE, informal) goodbye: Cheers then. See you later.
3 (BrE, informal) thank you

The Longman Web Dictionary also produced similar results, indicating that the term was used specifically in British English. (http://www.ldoceonline.com/dictionary/cheers)

cheers

1 used when you lift a glass of alcohol before you drink it, in order to say that you hope the people you are drinking with will be happy and have good health

2 British English informal thank you

3 British English informal goodbye

A search of the Cambridge Advanced Learners Dictionary showed no results. I cannot explain why this term was found in one British English Learner Dictionary but not in another. Perhaps my dear readers can help me on this by commenting? I do think that it is not found in the more 'standard' Oxford English Dictionary and found in the Oxford Advanced Learner's Dictionary, as it is an informal term that will probably not be used in formal speech but is still required for learners of the English Language to be acquainted with in order to possess sufficient Linguistic Capital to use the language effectively to communicate seamlessly with the native speakers.