Relevanssi

Relevanssi replaces the standard WordPress search with a better search engine, with many features and configurable options. You’ll get better results, better presentation of results – your users will thank you.

Relevanssi on WordPress.org

One features, relevancy offers, is the option to add stop words, words you don’t want to trigger search hit.

Say, I don’t want this post to be found when searching for “pinot”, as this blog isn’t about wine, I would at that word to the stop list, and it would be ignored.