One amusing usage error is when people use tenant when they mean tenet. A tenant, of course, is someone renting a property, while a tenet is “a principle, belief, or doctrine generally held to be true.”
Do you know the difference between something that’s historic and something that’s historical? These do in fact mean different things! Historic refers to something that has a big impact on history – say, for example, the historic first landing on the moon.
Another pair of commonly confused words is complementary and complimentary.
There are so many words that are spelled similarly to each other and therefore frequently get mixed up in writing. One of the most common pairs of these words is effect and affect. And while most writers usually know the difference between them, sometimes these words still get confused.