"Vicissitude"

From the OED:

The fact of change or mutation taking place in a particular thing or within a certain sphere; the uncertain changing or mutability of something; OR A change or alteration in condition or fortune; an instance of mutability in human affairs.

From Google:

The OED includes something they call "Frequency Bands" with each of their definitions. This metric helps to convey how frequently a word is currently being used in the English language, which types writing it appears in and whether is it beginning to show signs of fading away. From the page linked above: "Each non-obsolete word is assigned to a frequency band based on its overall frequency score. Bands run from 8 (very high-frequency words) to 1 (very low-frequency). The scale is logarithmic: words in Band 8 are around ten times more frequent than words in Band 7, which in turn are around ten times more frequent than words in Band 6."

"Vicissitude" is a Frequency Band 5 word: "This word belongs in Frequency Band 5. Band 5 contains words which occur between 1 and 10 times per million words in typical modern English usage. These tend to be restricted to literate vocabulary associated with educated discourse, although such words may still be familiar within the context of that discourse..."