Capable of being advertised; suitable or worthy of being advertised or promoted publicly.
From advertize (alternative spelling of advertise) plus -able meaning 'capable of being.' This word follows the standard English pattern of creating adjectives that express capability.
Not everything is advertizable—some products are so boring or shameful that companies struggle to make them seem appealing, which is why you'll notice that toilet paper commercials are hilariously creative just to make the product seem interesting.
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