Gum up Definition 1 of 2Pro Tip 1/3Physical Obstruction Used when something physical causes a device or tool to stop working correctly. The printer got gummed up with paper pieces. Pro Tip 2/3Colloquial Usage Commonly used in informal situations, such as casual conversation or storytelling. The old gate was gummed up with rust and wouldn't open. Pro Tip 3/3Metaphorical Extension Can be used metaphorically to describe non-mechanical things that are slowed down or hindered. My thoughts are gummed up from lack of sleep.