1. One dictionary I use is the Oxford English Dictionary. I have the app on my phone. I use the free version so I have to click through an ad once every few searches. It gives regional use. It also indicates whether a word is "informal", for example "butt-dial". It does not give enough to answer your specific question when you select "butt [3rd definition]". 2. For some questions, I use The Corpus of Contemporary American English english-corpora.org/coca/ In my text here, I am using quotation marks to be able to show details, but in your actual search use only what is between the quotation marks. Search "butt" and get lots. Search "rifle butt" and it will search for that exact string including the space between "e" and "b". You can see that many instances are from fiction and magazines and only one from an academic journal. Search with an asterisk, "*", as a wild card. It will give you all instances with anything where the asterisk is. Search "*butt*" and you get "butterfly", "push-button", "scuttlebutt", and others. If this doesn't answer your current question, maybe it will be useful in the future.

I also use WordReference.com

"the butt of a rifle". Hi Maria, is this what are You looking for? I fond it in the Merriam- Webster dictionary. Google translete butt-задница also offeer my a part of rifle. 😀

Did you try www.merriam-webster.com?