Here's a good one for today. A few weeks ago I went to a talk, and on one of the speaker's slides there appeared the phrase "osculating Cartesian covariance". I had no idea what that was, but since "osculate" means "to kiss", I was pretty sure that he'd meant "oscillating" instead.
So, feeling fairly smug, I was mentioning the error to my coworker afterwards when a bystander said, "Actually, 'osculating' is the correct term there." I was embarrassed and rather puzzled as to what it could possibly mean, so I looked it up. Indeed, there is such a thing as an osculating orbit, which is the orbit a celestial body would travel around its primary gravitational influence in the absence of perturbing forces like other planets or satellites. The term comes from the fact that at any point in time and space, a body's osculating orbit is tangent to (i.e. touches or "kisses") its actual orbit.