I have come upon the sentence with the word that I cannot get in Crash Course Anatomy & Physiology. It is at around 46 seconds. Here is the context:
Astronauts often experience things like trouble sleeping, puffy faces, and loss of muscle mass, but perhaps the most serious damage a microgravity environment causes is to the bones. And bones, well, they're pretty clutch.
I have looked up the meanings of the adjective clutch in a bunch of dictionaries, but none seems to fit.