Velocity

Velocity is usually treated as interchangeable with speed, but in the context of science, velocity is used to refer to a combination of speed and direction. There are a few different ways to express velocity. You might say you were driving 50 mph at 37 degrees from north per your compass. Or you might say, equivalently, that each hour you’re 40 miles farther north and 30 miles farther east. So, where with speed you could just give a single number, velocity requires a set of numbers that together give speed and direction. We call the former a scalar, and the latter a vector. Scalars are just normal numbers, but vectors are usually expressed like <50, 37°> or (40; 30). The symbols vary, it’s the grouping that’s important. 

The word, velocity, comes from the Latin vehere - to carry. This meaning is better preserved in biology where a vector is a disease carrier like a rat or mosquito. But the first recorded use in English was actually the mathematical version discussed above. It came about as astronomers were analyzing the elliptical lines that seemed to carry the planets around the sun. The velocity of the planet is, at each point, tangent to that elliptical line.