blis·ter / ˈblistər/ • n. a small bubble on the skin filled with serum and caused by friction, burning, or other damage. ∎  a similar swelling, filled with air or fluid, on the surface of a plant, heated metal, painted wood, or other object.• v. 1. [intr.] form swellings filled with air or fluid on the surface of something: the surface of the door began to blister [as adj.] (blistered) he had blistered feet. ∎  [tr.] cause blisters to form on the surface of: a caustic liquid that blisters the skin.2. criticize sharply: they came out and blistered the girls for pulling leaves off a chestnut tree.

blister A raised, well circumscribed lesion of the skin, containing a sterile fluid, derived from the serum. Strictly, a blister or bulla has a diameter of greater than 5 mm, smaller lesions being called vesicles. Commonly they become infected and fill with pus, and are then known as pustules. They are caused by trauma (friction, burns, and scalds), allergic contact dermatitis, insect bites, sunburn, etc. In earlier times agents were used to raise vesicles or blisters on the skin to relieve the pain from deeper structures by the process of counter-irritation. A commonly used vesicant was a powder derived from the pulverized dried beetles of Lytta vesicatoria, containing cantharidin, and commonly known as Spanish Fly or Blistering Beetle.

Alan W. Cuthbert

blister sb. XIII. ME. blister, blester, of unkn. orig.; poss. — OF. blestre, blostre swelling, pimple.
Hence blister vb. XV.

blister (blis-ter) n. a swelling containing watery fluid (serum) and sometimes also blood (blood b.) or pus, within or just beneath the skin.