Tenure

Etymology

From Latin "tenere" (to hold), by way of Old French "tenure" (a holding). It first described the conditions under which one held land or office. The modern academic sense — a permanent post protecting free inquiry — is a specialized flowering of that older idea of secure holding.

noun · /TEN-yer/
The length of time one holds a position, or a guaranteed, hard-to-revoke status in a job.
What it names
Both simple longevity and the special security — famous in academia — that shields someone from easy dismissal.
Example
After a decade’s tenure at the firm, she knew where every unwritten rule was buried.
Related idea
Tenure is time held or security of holding; attrition is the slow loss of people who don’t stay. High tenure and low attrition often travel together, but a place can have long-tenured veterans while bleeding newcomers.