blister (n.) Look up blister at Dictionary.com
c.1300, from O.Fr. blestre "blister, lump, bump," perhaps from a Scandinavian source (cf. O.N. blastr "a blowing," dat. blęstri "swelling"), or from M.Du. blyster "swelling;" perhaps ult. from PIE *bhel- (2); see bole. The verb meaning "to raise blisters on" is from late 15c.