flagship

flag +‎ ship

• IPA^(key): /ˈflæɡʃɪp/

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flagship (plural flagships)

1. In a maritime fleet, the ship occupied by the fleet's commander (usually an admiral); it denotes this by flying his flag.
2. The most important one out of a related group.

   The retail company's store in London is their flagship.

   • 2017 October 2, Jess Cartner-Morle, “Stella McCartney lays waste to disposable fashion in Paris”, in the Guardian‎:

     Next year, Stella McCartney’s London flagship store will move from Bruton Street to a landmark Old Bond Street location. The move is the most prominent symbol of the label’s strong financial results.

The word flagship is often used as an attributive noun, as in:

The company’s shop in London is their flagship store.

Although this usage looks like an adjective, it is not, and should not be confused with that part of speech.

• (most important one): chief, primary, principal, showcase