deteriorate
/dɪˈtɪərɪəreɪt/
verb
[no object]
Become progressively worse.
Origin
Late 16th century (in the sense ‘make worse’): from late Latin deteriorat- ‘worsened’, from the verb deteriorare, from Latin deterior ‘worse’.
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Emmanuel's accumulated linguistic acumen attracted attention early, but degraded and deteriorated over time. (Hiz skillz got worser.)