In many text mining or natural language processing applications, you will have problems with words that are very similar, but which are counted separately. An example might be the words win, winner, and winning. You can combine these words into a single category using stemming. This blog post gives a nice overview of stemming.
Bernhard Learns. Cleaning Words with R: Stemming, Lemmatization & Replacing with More Common Synonym. Blog post. April 27, 2017. [Link is broken]
You can find an earlier version of this page on my blog.