As Webster 1913 claims below, "tup" can mean to butt as a ram does, or simply a male ram or sheep. There is another definition though that is left out.

One night I was playing Scrabble with my wife. To not make the game as intense, and oh so much more educational, we often play with an "open dictionary" rule. As usually happens I was ahead by an ok margin going into the last few moves so my wife began a long hunt for a magical place to use her last few letters. Well, in this process she decided "tup" might just be a word. And this is what she discovered in the dictionary:

TUP v TUPPED, TUPPING, TUPS
to copulate with a ewe

We found this extremely amusing. After mulling over the idea for awhile someone came up with this important question:

So what is Tupperware for?