The Most Important Word in Science

As school subjects, biology, chemistry, physics, geology, astronomy, and meteorology take the cake when it comes to introducing volumes of new vocabulary words and terms to novice learners. (See my post on the Languages of Science)

Yet, there is one word common to all branches of science that ranks at the top of the list. A word so important that all the others probably would not exists without it. Can you guess what this word is? Scroll down for the answer.

why?