This is a really strange one, even in a series of strange words. Originally from Old French and meaning to gallop or run well, it took a turn for the worse in the early 1800s when it came to mean to thrash or, as a noun, a heavy blow. So to wallop someone or something or give them a wallop. Or give them a good trouncing. It also apparently meant the ‘noise of a boiling liquid’. But back to the gallop. To wallop is also to run clumsily, heavily. Another wonderful word with the same meaning is ‘lolloping’: the dog was lolloping along the beach. You might also say it was a walloping great dog, if it was a large breed like a St Bernard. So then it would be a walloping great dog lolloping along the beach. Love it!
If a book or a film packs a wallop, it has a big impact on you. If your drink packs a punch, you’re probably drinking beer (also known as wallop). And if your team loses, they’ve taken a walloping.
There is also mention of it having once meant a thick piece of fat, but since I just started dieting today, I’m going to ignore that.
There are English villages in Hampshire (confusingly abbreviated to Hants, so now you know) called Middle Wallop, Over Wallop and Nether Wallop (the last of which sounds too much like a smack on the bottom to be taken seriously!).