You can use truncation to find variations of a single term. In Gerritsen Online, use a ? at the end of your term to match all terms with a single additional letter or number, and use a * at the end of your term to match all terms with more than one letter or number. For example,
literat?
will retrieve results containing 'literate' and 'literati', but not 'literature',
while
literat*
will retrieve results containing 'literate', 'literati' and 'literature'.