Thank you for your post.
There are many ways to accomplish this. However, since you are a newbie, I would suggest starting slowly and get to know the inner workings of FileMaker Pro. Therefore, I would create a field for the part of speech, and then have three separate fields for each variation of the word. If you use a verb, you would only use the first two variation fields, while if you use an adjective, all three variation fields would be used.
Pull down the View menu and select "Layout Mode". If you double-click on the part of speech field, you set the field to be a Pop-up or Drop down with a set of values. Create a Value List with the values "Noun", "Verb", and "Adjective". Return to Browse Mode (from the View menu) and when you select the part of speech field, you either get a Pop-up menu or a drop down menu with the three values. This will help in staying consistent with your entries, and you don't have to type it in each time. Select the correct part of speech and move to the next field.
Pull down the View menu and select "Find Mode". Select the pop-up/drop down part of speech field, and you can search for all Nouns, verbs, or Adjectives.
Once you understand these concepts, then your next step is to look at relating a table to another table - one of the key components of a relational database system. I would rather not go into it at this time...
Let me know if you need clarification for any of the above steps.