Main Entry: re·agin

Pronunciation: \rē-ˈā-jən, -gən\

Function: noun

Etymology: International Scientific Vocabulary, from reagent

Date: circa 1911

1 : a substance in the blood of persons with syphilis responsible for positive serological reactions for syphilis
2 : an antibody (as IgE in humans) that mediates hypersensitive allergic reactions of rapid onset

— re·agin·ic \ˌrē-ə-ˈji-nik, -ˈgi-\ adjective