Hi, only related words can have multiple items; keyword names can’t (unless you want the whole thing to be added as a tag, which is probably not the case).
If I understand you correctly and you want APT to add multiple tags to posts if certain related words are found, probably the easiest solution is creating several different keywords with the same related words.
If you have a lot of these keywords, I would suggest using some spreadsheet software to assign all the related words to each keyword (in MS Excel or OpenOffice Calc you can do this with just a few clicks), and then importing the data to APT as a CSV file.