The meaning of life in one word?
Well, sort of …
• It matters
• What matters
• Mattering – you matter
So, matter, matters, mattering … 
Matter: Connection requires stuff. Matter is stuff. Without stuff, nothing matters.
It matters: The fact that there’s stuff and that we emerged from that stuff (stardust) places everything in a context, an import for being.
What matters: Interactions & relationships – at every scale from the cosmic (10^n) to the local, interpersonal, and personal – set the stage for valued connections. Dependence and interdependence.
Mattering: Within more immediate connections and interactions, each of us matters. 
 My working one-word answer for some time has been “connection.” But a recent article noted: “Increasingly a consensus is building that mattering stands on its own in psychological terms” – regarding mental health. Perhaps social health, a society’s health, as well.
While possibly available from several sources, this article was published as “Do You ‘Matter’ to Others? The Answer Could Predict Your Mental Health” by Scientific American on 10-6-2022.
 With the caution that mattering has a darkside. Life (and history) is full of examples where mattering is pathologically twisted. Preying upon “people’s need to feel valued and seen by others as important.”