[W/K] :: nidus

  Nidus \Ni"dus\, n.; pl. nidi. [L. See Nidi, Nest.]
     A nest: a repository for the eggs of birds, insects, etc.; a
     breeding place; esp., the place or substance where parasites
     or the germs of a disease effect lodgment or are developed.
     [1913 Webster]

  nidus
       n 1: a central point or locus of an infection in an organism;
            "the focus of infection" [syn: focus, focal point]
       2: a nest in which spiders or insects deposit their eggs
       [also: nidi (pl)]