ulcer

n. open sore accompanied by pus and disintegration of surrounding tissue (Pathology); cause of corruption, moral blemish

An ulcer (from Latin ulcus) is an open sore of the skin, eyes or mucous membrane, often caused, but not exclusively, by an initial abrasion and generally maintained by an inflammation, an infection, and/or medical conditions which impede healing. In other words, it is a macroscopic discontinuity of the normal epithelium (microscopic discontinuity of epithelium is called erosion). Other causes of skin ulcerations include pressure from various sources and venous insufficiency.
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Ulcer /ul·cer/ a local defect, or excavation of the surface, of an organ or tissue, produced by sloughing of necrotic inflammatory tissue. [more]Ulcer - Community and Resources

Noun
1. a circumscribed inflammatory and often suppurating lesion on the skin or an internal mucous surface resulting in necrosis of tissue
(synonym) ulceration
(hypernym) lesion
(hyponym) aphthous ulcer
(derivation) ulcerate

(v. t.)
To ulcerate.
  

(n.)
Fig.: Anything that festers and corrupts like an open sore; a vice in character.
  

(n.)
A solution of continuity in any of the soft parts of the body, discharging purulent matter, found on a surface, especially one of the natural surfaces of the body, and originating generally in a constitutional disorder; a sore discharging pus. It is distinguished from an abscess, which has its beginning, at least, in the depth of the tissues.