Your reasoning about relying on dictionaries makes sense. In addition to that, many proper nouns can be used adjectivally. Some examples: a Marlon Brando movie, a London theatre, a Liverpool train.
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CliveHi guys,Hi Clive
It's not just proper nouns. eg a car wash, a car door, a book club, a kitchen table.
You might refer to a grammar book for details/guidelines on doing this, eg Michael Swan's Practical English Usage, Section 21 on 'nouns used as adjectives' and Secton 424 on 'nouns in groups'.
Best wishes, Clive