To make something unpopular or to reduce the popularity of something.
From 'dis-' (reverse, make not) + 'popularize' (from 'popular' + '-ize' suffix). A modern formation following standard English word-building patterns.
This word is so rare that it's almost never used—we usually say 'decrease in popularity' instead—but it's a perfect example of how English lets us build almost any word we can logically imagine, even if practicality disagrees!
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