precipitin
noun
pre·cip·i·tin pri-ˈsi-pə-tən 
: an antibody that forms a precipitate when it unites with its antigen
Word History
Etymology
International Scientific Vocabulary, from precipitate
First Known Use
1900, in the meaning defined above
Medical Definition
precipitin
noun
pre·cip·i·tin pri-ˈsip-ət-ən
: any of various antibodies which form insoluble precipitates with specific antigens and some of which are used in serological testing