If you want to find a word in a corpus, then you need full text search capabilities. SQLite does actually offer such capabilities as an extension, which are explained here.
Full text search is going to return the document that matches a given query. You will first need to break up the corpus into separate documents. Usually, this is a very easy task -- the documents might be emails, or customer service records, or doctor's notes, or reports, or whatever. However, you do not describe what the documents are in your case.
I am not at all familiar with the full-text extensions to SQLite. You might consider other database solutions like MySQL which also offer full text support.