un·der / ˈəndər/ • prep. 1. extending or directly below: vast stores of oil under Alaska the streams that ran under the melting glaciers. ∎ below (something covering or protecting): under several feet of water a hot plate under an insulated lid. 2. at a lower level or layer than: the room under his study. ∎ behind (a physical surface): it was written on the new canvas under a gluey coating. ∎ behind or hidden behind (an appearance or disguise): he had a deep sense of fun under his quiet exterior. ∎ lower in grade or rank than: under him in the hierarchy. 3. used to express dominance or control: I was under his spell. ∎ during (a specified time period, reign, or administration): it occurred under the pontificate of Paul II. ∎ as a reaction to or undergoing the pressure of (something): the sofa creaked under his weight certain institutions may be under threat. ∎ as provided for by the rules of; in accordance with: flowers supplied under contract by a local florist. ∎ used to express grouping or classification: file it under “lost” published under his own name. ∎ Comput. within the environment of (a particular operating system): the program runs under DOS. 4. lower than (a specified amount, rate, or norm): they averaged just under 2.8 percent. 5. undergoing (a process): under construction. ∎ in an existent state of: children living under difficult circumstances. ∎ planted with: fields under wheat.• adv. 1. extending or directly below something: weaving the body through the crossbars, over and under, over and under. 2. under water: he was floating for some time but suddenly went under.• adj. 1. denoting the lowest part or surface of something; on the underside: the under part of the shell is concave. 2. unconscious, typically as a result of general anesthesia: the operation was quick—she was only under for 15 minutes.PHRASES: go undersee go1 .under way having started and making progress. ∎ (of a boat) moving through the water: no time was lost in getting under way. DERIVATIVES: un·der·most / -ˌmōst/ adj.ORIGIN: Old English, of Germanic origin; related to Dutch onder and German unter.