Atrophy
Etymology
From Greek atrophia, "a wasting away for want of food," from a-, "without," plus trophe, "nourishment." It entered English as a medical term for tissue that shrinks when starved or unused. The figurative sense — skills or institutions withering from neglect — follows the same logic of decline through deprivation.
noun · /AT-ruh-fee/
The wasting away or shrinking of something from lack of use or nourishment.
What it names
The specific decline that comes not from attack but from disuse — a muscle, skill, or faculty that dwindles because it was never exercised.
Example
Months of remote work led to a quiet atrophy of the small talk skills she had once taken for granted.
Related idea
Decay can strike something in active use, driven by rot or damage; atrophy specifically implicates disuse or starvation as the cause of the shrinking.