n, pl  species  1 a  :  a category of biological classification ranking immediately below the genus or subgenus, comprising related organisms or populations potentially capable of interbreeding, and being designated by a binomial that consists of the name of the genus followed by a Latin or latinized uncapitalized noun or adjective agreeing grammatically with the genus name  b  :  an individual or kind belonging to a biological species  2  :  a particular kind of atomic nucleus, atom, molecule, or ion <production of DNA damage by active oxygen >  .
 
   
 
Similar sounding terms:  sep·sis 
 
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