Once you have identified the main concepts in your search question, the next step is searching comprehensively is to identify synonyms for each of your concept. What are all the ways authors might express the concepts you're interested in?
The only way to find key outliers in the literature is to think of all the ways authors might describe your concept-- without going beyond the scope of how you've defined them. How will you find this balance?
There are many types of synonyms to consider when generating synonyms for your search strategy:
Terms that have the same/close meaning:
Terms that have different spellings or acronyms:
Complex concepts described inconsistently:
Umbrella terms and specific names:
Keywords and database-specific “subject headings”:
Discipline-specific jargon and surrogate terms:
Wikipedia is your Friend.
Is your search term or concept called anything else? Look it up in an encyclopedia to find out.
For example, in the wikipedia entry for "hypertension", the synonym high blood pressure is quickly identified in the opening sentence. This is true for most wikipedia entries for scientific and medical terminology. It is wikipedia, so exercise caution when using this as a background reading source.
You can also easily find synonyms in other background sources, including your lecture notes, as well as textbooks and print encyclopedias (yes! they still exist!) which you can find via the library catalogue.
Background sources can also help you find umbrella terms and specific terms, as well as provide you with the kind of contextual information on a topic that always comes in handy when you're searching!
Mine Relevant Articles for "Subject Headings"
Let's say you have a relevant article on a topic. You could have this before you start a search, or it could come from early first attempts at searching, or maybe it's from your reading list.
You can find out how this article is indexed in controlled vocabulary databases by searching for it by title in Medline or CINAHL and opening the article's complete record. In CINAHL, the subject headings will be listed as Major and Minor subjects; in Medline they will be listed under MeSH Subject Headings.
"Used For" terms in controlled vocabulary databases
Look at a MeSH subject heading's scope note to check its used for terms. For instance, the used for MeSH term for 'cancer' is 'neoplasm'.