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1. To continue in a manner that feels interminable or tedious. After Susie's presentation ground on for 45 minutes, the teacher finally told her to wrap it up.
2. slang To dance very closely to someone while using aggressive and overtly sexualized hip movements. In this usage, one of the participants is named after "on." If one more skeezy guy tries to grind on me, I'm out of here! Why would I go to a school dance? To watch all the cool kids grind on each other all night?
Fig. [for something] to drag on endlessly. The hours ground on without anything happening. I was so tired of waiting. The lecture ground on, minute after minute.
ground something on something
Fig. to build a firm basis for something on something else. He grounded his thinking on his detailed research. His thinking was grounded on years of reading.