Synonyms are other words that have the same meaning as your keywords; think of words or terms that may be used interchangeably. You may want to add some of these terms to your keyword list. Include alternate spellings or forms of your keywords. What other words or terms are related?
Example:
Gas, gasoline, fuel, fossil fuels,
United States, America, USA
Prices, cost, expense
economy, finances, economic, fiscal, inflation
etc.