Here are a few more terms writers have confused or misused in the material I've read recently:
Everyday vs. every day
Wrong: He does this everyday.
Right: He does this every day.
"Everyday" means typical or ordinary, not reserved for special days. In California, enjoying the sunshine is an everyday occurrence. It's something you can enjoy every day.
Tact vs. tack
Wrong: "I couldn't draw like a professional, so I had to take a different tact."
Right: "I took a different tack."
"Tact" is a noun meaning the ability to say things in a way that is not offensive or hurtful.
"Tack" is a noun for changing a sailboat's course by turning the boat's head into the wind. From that it also became a noun for a course of action or policy. (It also has a few other unrelated meanings.)
