When discussing physics it is often useful to distinguish between particles that have mass (such as protons and electrons) and particles that have no mass (such as photons). In English it is easy to categorize the latter - we can call them "massless" particles. But what about the former? The term "massive" evokes something enormous, several millions (if not billions or trillions or more) orders of magnitude greater than a mere proton. So what adjective can we use (or is being used) to describe particles that have mass? I realize this is a question as much for linguists as it is for physicists, but I though I would ask here first.