There are many words which take a very different meaning in their scientific context to what they might mean in everyday use.
One which always amuses me a little is “massive”.
Normally, when you call something massive, you mean it’s really rather large. You might look at me in bemusement if I call an electron “massive”. You may wonder what on earth an electron is big compared to. (The answer to that is: nothing, really. The electron is generally considered to be a point particle.)
What I actually mean is that the electron has mass. An electron is massive. An atom is You are massive. A photon is massless.
Massive: it doesn’t have to be big, it just has to have a non-zero mass.