An event, usually unwanted, sometimes in the sense of a penalty. Unlike risk, which has a number attached to it (it's quantitative), a hazard is 'yes' or 'no': it's either realised, or experienced, or it's not; although one hazard can be worse to experience than another, you can't put a figure on it (it's said to be qualitative).

A controversial and emotionally hazardous way of dealing with a higher-order multiple pregnancy (such as quadruplets, quintuplets, or higher) in which, all the embryos or fetuses are at risk of being lost before viability. The technique involves carrying out transvaginal ultrasound and injecting a lethal substance (such as air or a solution of potassium) into the visibly beating heart of one or more of the embryos, so reducing the number of surviving embryos to three, two or one. Generally regarded as a more stressful procedure than even an induced abortion, both for the person undergoing the operation and for the ultrasound doctor asked to do it. Few people regard the availability of fetal reduction to mean that the greatest care does not need to be taken to avoid higher-order multiple pregnancies in assisted conception programs. There's a hazard: loss of the remaining fetuses from miscarriage; but the risk of this, with an experienced ultrasound doctor or fetal medicine specialist, is low.