deterioration
n.the process of becoming worse in quality or condition. You use this word when something gradually loses its value, strength, or health.
n.the process of becoming progressively worse in quality, value, or condition; decline.
“The deterioration of the old bridge worried the town council.”
“Doctors noted a rapid deterioration in his health after the surgery.”
“The slow deterioration of the manuscript's ink made it nearly impossible to read the final chapter without special lighting.”
“At first, I failed to recognise the significance of the deterioration in my violin technique.”
“We have not found measurable acceleration of rock deterioration linked to current pollution.”
Borrowed from French détérioration; morphologically deteriorate + -ion.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.