per·ni·cious / pərˈnishəs/ • adj. having a harmful effect, esp. in a gradual or subtle way: the pernicious influences of the mass media.DERIVATIVES: per·ni·cious·ly adv.per·ni·cious·ness n.ORIGIN: late Middle English: from Latin perniciosus ‘destructive,’ from pernicies ‘ruin,’ based on nex, nec- ‘death.’

pernicious (per-nish-ŭs) adj. describing diseases that are highly dangerous or likely to result in death if untreated. p. anaemia a form of anaemia resulting from deficiency of vitamin B¹², due either to failure to produce intrinsic factor or to dietary deficiency of the vitamin. It is characterized by defective production of red blood cells and the presence of megaloblasts in the bone marrow.

pernicious XVI. — L. perniciōsus, f. perniciēs destruction, f. PER- + nex, nec- death, destruction; see -IOUS.