Natural killer cell means: The natural killer cell is a cell that reacts against or destroys another cell, without being sensitized to it. Abbreviated NK cells. NK cells form part of the first line defense against viruses-infected and cancer-cells. Small lymphocytes called NK cells originate from the bone marrow. They develop independently of the influence of the Thymus. A NK cell attaches itself to a target cells and releases chemicals to break down its cell walls, causing it to lyse.
(in Medical Dictionary)

What else does Natural killer cell mean?

Double-stranded DNA or lymphokines activate lymphocytes and kill viruses and tumors.
(in Merlin Dictionary)