There is no way to immediately delete a metric/tag. Unused metrics/tags “age out” of the UI naturally after 12 hours.
With respect to monitors, the metric stream will stop being considered after that age-out period.
With respect to dashboards, the metric/tag will still appear in the visualizations following the age-out period, but will not be available in the dropdown menus for graphing via our UI. The corresponding metric + tag space remains available for graphing using the JSON method.
If you’re running the Agent, and assuming you’ve intentionally stopped or removed your host, all hosts and metrics that have not seen new data in 12 hours will disappear from the UI. You may still query against them, however, they will not appear in drop downs, nor in the infrastructure or host map views.