The top 10 trending keywords registered in .COM and .NET domain names during the month of May 2018 were published by Verisign, the .com and .net registry.
There were 2 common keywords in the 2 lists: sports and bet
You can find the list from last month here.
My experience shows that 700 or 800 (or even less) domain registrations are enough to bring a keyword into the top 10.
Top 10 Keyword Registration Trends for .COM and .NET in May 2018:
*Note: Each list was developed by examining keyword registration growth relative to the preceding month, such that those keywords with the highest percentage of registration growth are being reported on. This method is used to eliminate commonly registered keywords, such as “online” and “shop,” to provide a true look at monthly trends. In order to be included, a keyword must experience a minimum threshold in registration growth month over month. Qualifying keywords with the highest volume of registrations are then ranked and included in the list.
If you’d like to do your own domain name keyword research, check out Verisign DomainScope, a tool that allows you to enter keywords to see registration trends in .com and .net.