A recent post listed and defined words with the Greek prefix hyper– (meaning “above,” “beyond,” or “over”). Here, words based on its antonym, hypo-, are the focus.
The most common words beginning with hypo– include hypodermic (literally, “under skin”), an adjective describing injection under the skin or tissue or growths beneath the skin (the word is also employed as a noun, and hypo is a common truncation), and hypothermia (“under heat”), the term for abnormally low body temperature.
Other medical conditions include hypoglycemia (“under sugar blood”)—colloquially known as “low blood sugar”—and hypochondria (“under cartilage”), mental depression in which the sufferer imagines physical ailments, so named from the original belief that such feelings originated in the abdominal organs; the term for the pathological state is hypochondriasis. Hypochondriac is both an adjective describing the condition and a noun pertaining to the sufferer.
Hypoallergenic means “unlikely to cause an allergic reaction,” and the hypothalamus is a key part of the brain that regulates automatic processes in the body. Oxygen deficiency is called hypoxia, and hypomania is a mild mania associated with bipolar disorder. (The respective adjectives are hypoxic and hypomanic.)
Other well-known words in the hypo– family are hypocrisy (“under decide”), which evolved in meaning in Greek from “sift” to “play a part” and now describes actions or attitudes that contradict one’s stated beliefs or opinions, and hypothesis (“under proposition”), which denotes something assumed and taken for granted for the sake of argument; the plural is hypotheses. One who demonstrates hypocrisy is deemed hypocritical and called a hypocrite. The adjectival form for hypothesis is hypothetical, and the verb form is hypothesize.
A hypotenuse is the side of a right triangle opposite the right angle. (The root word is the basis of tension and tenuous.)
More obscure terms in this group include hypocorism (“under caress”), meaning “pet name,” as in a diminutive like Bobby, a term of endearment such as honey, or baby-talk forms of address such as papa; such words are hypocoristic. One who lives underground is hypogean (the antonym is epigean), and a hypocaust is a chamber for lighting a fire to heat rooms located above. (The root is the same as that seen in holocaust.)
A disguised relation is hyphen—literally, “under one,” because the mark was originally located beneath the words to be connected.