Using a checkbox to reference database synonyms? C#

sorry if this is an easy fix im very new to programming and having a bit of trouble but will try to explain best i can. Currently i have a winforms project where i select any directory within my first text box and all sub directories and files show in a list box. After which i search for a term in my 2nd text box, and the list box returns any files containing that term. Now i have connected a data source that has two rows, word and synonym. What i want to do is have a checkbox that says "include synonyms" and when clicked, searching for a term will also return any files containing the corresponding synonyms within the connected data source. Im not quite sure how to do this and am really just stabbing in the dark, any help would be much appreciated. Thank you!