A semordnilap is a word that when spelled backwards makes a different word.
“Boom, boom boom, Mr. Soft! Won't you tell me why the world in which you're living, is so strange!”
If you're a certain age, then you'll remember the hilarious Mr. Soft advert - check it out here on YouTube for a reminder:
Why am I mentioning this you say? Well, the product that he's advertising are softmints, and are made by a company called Trebor. What does Trebor spell backwards? It spells Robert!
It gets spooky too, as my brother is called Robert and he looks a lot like Mr. Soft!
See below more examples of semordnilaps, where one word spells a different word backwards: