I recall my first public law class very fondly, because of this word. It kept appearing in the slides and the readings, but I had no idea what it meant. I did some online searches for it, but Wikipedia and other sites gave no clean definition. But in class, when the tutor asked, “What is constitutionalism?”, I took a random stab at the answer, “Limiting government power.” I was surprised when the tutor said that I was right, and this turned into the simple definition we went back to for the whole class.
But with some hindsight, I realise why the word accords no simple definition. Even the simple definition I gave wasn’t entirely accurate, because it assumes that government power will be limited. This is not always the case, yet for some reason governments face limits? It’s confusing. But hey, hope the simple definition works for you.