n 1  :  a substance that is in the blood of individuals with syphilis and is responsible for positive serological reactions for syphilis  2  :  an antibody that is in the blood of individuals with some forms of allergy and that can passively sensitize the skin of normal individuals re*agin*ic adj 
 
   
 
Similar sounding terms:  re·gion 
 
Published under license with Merriam-Webster, Incorporated.  © 1997-2024.