Here is the basic and obvious post of the day but hey, always good to go back to basics every now and then. One webmaster asked if Google may treat plural and singular words as different keywords and John Mueller of Google said yes, Google can.
John responded on Twitter, here is the set of tweets:
@bharatkataria yes, they can be.
— John Mueller (@JohnMu) July 27, 2016
Sometimes Google will show one or the other and sometimes not.
It depends and that is why you need to try different things and make sure to understand how your prospects will search for your products and services.
Forum discussion at Twitter.