Medical Definition of patch
1a: a piece of material used medically usually to cover a wound or repair a defect—see patch graftb: a usually disk-shaped piece of material that is worn on the skin and contains a substance (as a drug) that is absorbed at a constant rate through the skin and into the bloodstream <a nicotine patch>—called also skin patchc: a shield worn over the socket of an injured or missing eye
2: a circumscribed region of tissue (as on the skin or in a section from an organ) that differs from the normal color or composition <sometimes great white patches develop on the tongue, the cheeks, and the gums—Morris Fishbein>
Seen and Heard
What made you want to look up patch? Please tell us where you read or heard it (including the quote, if possible).