Hyper- - hypo-

Hyper- and hypo- are two prefixes derived from Greek. They are sometimes attached to the same root, as in the medical nouns 'hyperglycaemia', meaning "an abnormally high concentration of sugar in the blood" (with the corresponding adjective 'hyperglycaemic'); and 'hypoglycaemia', "an abnormally low concentration of sugar in the blood" (adjective 'hypoglycaemic'). It should be apparent that to confuse these two terms may be fatal for a patient who has entered a coma from the effects of diabetes: those caring for such patients must distinguish whether the treatment is to give more sugar or more insulin.

• hyper- (representing the Greek ὑπερ) means 'over', 'above', and consequently 'beyond [normal]' and 'excessive'. A 'hyperactive' child is one who uses more energy than normal
• hypo- (Greek ὑπο) means 'under', as in 'hypodermic', 'under the skin': a hypodermic syringe is designed to pierce the skin and introduce drugs into the flesh and blood beneath; and 'hypothermia', having a temperature far below normal.

The confusion between such similar-sounding elements with diametrically opposed meanings is paralleled with the pair 'sub-' (under) and 'super-' (over) from Latin. These are actually cognate forms.