Nice word! I've probably never heard it spoken actually.
This also falls into the same linguistic catacombs of having complex and rich information. Impermanence describes... first permanence, secondly the inverse of that.
Permanence describes "constancy", or "unchanging", or just as
@Spiny Norman says, "Certainty", but prefaced with an inverse property as "Uncertainty" or Impermanence.
Now I assume we understand each of these words we're referring to have more specific meaning on their own than I am crediting exactly, like there are more unique implications within each word.
But at the core, the fundamental expressions of what they represent, and whatever existential objectivity they exist of, is the same, or at least I would like to address the notion of that being the case.
However this description, "Impermanence" is more fundamental than @Spiny Normans because it gets right to the asymmetrical core using a single term rather than the two of Fragility and Uncertainty combined. The term fundamental refers to getting to the bottom of things, and how simple they can be.
So far, can you recognize how in some ways all of our different ideas of what is fundamental... is actually the same expression? And how the definitions of the words could possibly all be interpreted as I'm suggesting?