When you type keywords in the search, Google will bold the requested keywords as well as their synonyms. For example if you type Japanese cars, the synonyms like vehicles will be bold as well. But not all of them are bold, sometimes even car is not bold either.

Is there a certain rule when Google decide when to bold certain keywords and their synonyms? Is there a way to find out what synonyms use for each keyword?

2 Answers 2


Google search algorithm has progressed so that it look at latent semantic indexing, where it creates buckets of similar keywords that it will infer as having a shared meaning, particularly when used in conjunction with one another.

Whilst slightly outdated this article covers the way Google's synonym algorithm works and says that over 70% of searches are affected by the synonym algorithm. They explain that the way they decide whether to bold a synonym is:

Historically, we have bolded synonyms such as stemming variants — like the word "picture" for a search with the word "pictures." Now, we've extended this to words that our algorithms very confidently think mean the same thing, even if they are spelled nothing like the original term.

Google says that the same words may not always appear bolded because they analyse:

other words in your search and use many signals

They way that Google determines keywords that will fit in the various buckets is by:

Our systems analyze petabytes of web documents and historical search data to build an intricate understanding of what words can mean in different contexts

As I have said this article is slightly outdated, but seems to cover your question well. over the last 3 years this technology is likely to have been advanced significantly and the way they determine keywords is likely to have become significantly more accurate, however, the general principles will be similar

  • Is there a way of actually finding out what keywords are shared? Commented Aug 23, 2013 at 18:50
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    The third quoted extract suggests that it is down to the context that the word is used; this means that it is possible for the same word to be shown in both bold and not bold for the same search query; dependent on the context that the word is used. Google uses an algorithm to determine synonyms. They likely regard the algorithm as intellectual property, therefore they don't appear to explain precisely how it works, other than the broad explanation in the article as summarised above. Commented Aug 23, 2013 at 19:11

I see more synonyms being bolded on page two but that's probably different for everyone. If there is a rule or algorithm like any other which Google has, they won't give a specific answer.

Two good pages about how they use these are below

Matt Cutts blog More info about synonyms at Google


Google Blog Helping computers understand language

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