an ‧ a ‧ phy ‧ lac ‧ tic shock /ˌænəfəlæktɪk ˈʃɒk, ˌænəfɪlæktɪk ˈʃɒk $ -ˈʃɑːk/ BrE AmE noun [uncountable] medical
a very sudden serious physical reaction that is caused by an ↑ allergy to something such as nuts, eggs, or the ↑ sting of some insects. The reaction causes shock, breathing difficulties, and sometimes death.