Is it good to save Keywords stored by users in a new DB schema? My question is more from the schema design and of further performance of the DB.

I'm designing a DB schema which will store strings primarily. Actually, users work on these strings, as normal mortals, in macro-enabled Excel workbooks and there, they have one column specifically designed to store keywords so they can find words within a second column quickly.

Some of these words are obviously deduced. For example, if column 1 is the keywords column and column 2 is the text column, column 2 could say "information required for feature description" and, its keywords in column 1 would be "information", "feature" and "description".

So far so good, common sense, but there are texts that have, for example, "N", "S", "W", "E", as the four points of a compass but in the keyword column, instead of having "North", "South" and so on, the keyword for all is just "compass".

We could ask for a keyword change but it would be a little troublesome, so my question is, is it worth saving these keywords in the schema, whether there's a table for them or not, or is it better to get the keyword as the result of a query from the texts stored?

We know working with strings is difficult, would these affect performance in the future?

BTW, if it helps, I'm thinking of using PostgreSQL.
I would have 2 columns: one for the description and one for the keyword. 
I would probably use MyIsam (depending on which Mysql version you're using) and use Mysql FullText search features. Innodb supports it now. I would test with both and see which ones is most performant.