have a (good/solid/sound/etc.) grasp of/on (something)(redirected from have a good grasp on something)
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have a (good/solid/sound/etc.) grasp of/on (something)
To have a firm, clear understanding or determination of something. I hope everyone has a solid grasp of the material, as you'll be tested on it next week. I thought I had a pretty good grasp on English idioms, but I don't understand this one at all!