The definition on the Oxford Dictionary is a little bit confusing for me. The dictionary doesn't call it a proper noun, but the first letter is capitalised in the example.

Since I know the Underground as a transportation system specific to a place (e.g. London), I would expect it to be a proper noun. Checking the dictionary didn't help me.



  1. (often the Underground) British An underground railway, especially the one in London.

‘travel chaos on the Underground’

Is it a proper noun or a common noun?

  • Using the definite article, and thus defining the usage, makes the common noun proper. Thus 'the Underground' in London, the 'Subway' in Glasgow or the 'Metro' in Washington DC. – Nigel J Aug 10 '18 at 12:03

The definition does not say that the word "underground" is specific to London.

"The Underground" in London is a proper noun (that's why it's capitalized).
"The Metro" in Paris is a proper noun (again, that's why it's capitalized).

If you're talking about underground train systems in general, what word do you use in England? You can't use "subway" because it means something different. So you use "underground" or "metro" — they're both common nouns in this usage.

If you ask whether anybody actually uses "underground" for anything other than the system in London, it seems to be incredibly rare. But the dictionary definition clearly suggests that this is one possible usage, and it would be this usage that is a common noun rather than a proper noun.

  • @Peter Shor, there is only one Underground in Britain - it is in London. There is a Subway in Glasgow. These are underground railway systems or classic "metros". There is a Metro in Tyne and Wear, which is a light rail system. – Michael Harvey Aug 10 '18 at 12:46
  • @MichaelHarvey: The common noun would usually be used when talking about underground train systems in general, not when talking about one in a specific city. For example, from Google books: "(AST) has gained broad experience in the design and implementation of undergrounds in major Italian and European cities; these works often interact with sites and structures belonging to the historic and artistic heritage." – Peter Shor Aug 10 '18 at 12:56
  • Did you notice my capitalisation? – Michael Harvey Aug 10 '18 at 13:10
  • Emilio Bilotta, ‎Alessandro Flora, ‎Stefania Lirer are not English names; I suspect they are Italian. The use of 'underground' as a generic term is unusual in Britain. – Michael Harvey Aug 10 '18 at 13:16
  • Link here. I suspect most native English speakers in the U.K. would use "metro" for this meaning today, but the dictionary is also supposed to cover English as it was used earlier this century. – Peter Shor Aug 10 '18 at 13:17

Not sure if it's relevant to why you need to know this, but in London they far more frequently call that underground railway "The Tube," which is a proper noun and should be capitalized. If you were to say, "The Underground," this would also be a proper noun and should be capitalized, although this phrase is not as locally common and is more formal, perhaps more posh or pretentious.

If you are using "metro," "underground," or "subway" in general terms, and are not specifying a particular system in a particular city, these words are not capitalized.

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