Here is an example that illustrates how different words can be used for essentially the same topic. Pretend each item in the bulleted list is a newspaper headline:
Each headline essentially refers to the same age group of people (those words are underlined) and any of these articles could have been missed unless you thought to search for all five of the terms used to reference this age group. There are other examples as well: smoke, smokers, smoking, tobacco use.... Or for cancer: cancer, cancerous, neoplasm, carcinogenic.... Most of the time, a number of terms can be used for any simple search. The videos below will provide some ideas about coping with synonyms.