Occasionally, your content score may not reflect the usage of terms that you deem are equivalent. For example, you may be using a term with a hyphen, and Optimize sees it as two separate words. Or perhaps Optimize suggests the single version and you’re using the plural.
You can verify this manually by searching Google using both terms. In some cases, the SERP similarity shows high overlap. In other cases, it doesn’t.
That’s why MarketMuse is extremely cautious about bucketing terms if they are the same or similar.
So, if you’re using a term that you believe is equivalent, consider it used. But just make sure to verify the SERP similarity in Google. You may be surprised!