The Collaborative International Dictionary of English v.0.48:

Vesicatory \Ves"i*ca*to*ry\ (?; 277), a. [Cf. F.
   v['e]sicatoire.] (Med.)
   Tending, or having power, to raise a blister. -- n. A
   blistering application or plaster; a vesicant; an epispastic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

vesicatory
    adj 1: causing blisters [syn: vesicatory, vesicant]
    n 1: a chemical agent that causes blistering (especially mustard
         gas) [syn: vesicant, vesicatory]