The word is usually used in the context of war. See:

https://cyberbelli.com/2012/05/26/cyberspace-is-a-domain-of-...

http://ndupress.ndu.edu/Media/News/News-Article-View/Article...

http://www.academia.edu/1753317/A_Theory_of_War_in_the_Cyber...

Google trends is not good for this kind of analysis. Google trends is based on the number of searches for a particular term relative to all other searches. So you see the same trend when you look at other tech topics like Linux, programming, SSH, computer science, etc. It's not that these things are necessarily becoming less popular, just that tech oriented people were over represented on the early internet, and thus Google search. As more non tech people started googling stuff, tech topics fell in their relative importance.

Re-read the comment you replied to, cyber security is trending in the opposite direction of Cyber (or SSH). That would seem to invalidate your thesis; Cyber security is gaining popularity relative to other topics.

Edit: there's also an interesting spike in Google trends for "cyber" every November. National Cyber Security Awareness Month is in October.

There were two assertions made in tener's comment. The first was that the term "cyber" was going out of use, the second was that the term "cyber security" was increasing. My comment was referring to the first assertion.