<p><strong>Noun</strong></p><ul><li>a small metal instrument specially cut to fit into a lock and move its bolt.</li><li>any of various devices resembling or functioning as a key: the key of a clock.</li><li>something that affords a means of access: the key to happiness.</li><li>something that secures or controls entrance to a place: Gibraltar is the key to the Mediterranean.</li><li>something that affords a means of clarifying a problem.</li><li>a book, pamphlet, or other text containing the solutions or translations of material given elsewhere, as testing exercises.</li><li>a systematic explanation of abbreviations, symbols, etc., used in a dictionary, map, etc.: Compare legend (def 4).</li><li>a systematic tabular classification of the significant characteristics of the members of a group of organisms to facilitate identification and comparison.</li><li>a pin, bolt, wedge, or other piece inserted in a hole or space to lock or hold parts of a mechanism or structure together; a cotter.</li><li>a device for opening and closing electrical contacts.</li><li>a liquid, usually water, in which a medication is dissolved.</li></ul><p><strong>Adjective</strong></p><ul><li>essential; central; important: a key person in the company; key industries.</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>to regulate or adjust (actions, thoughts, speech, etc.) to a particular state or activity; bring into conformity: to key one's speech to the intellectual level of the audience.</li><li>to adjust the colors in (a painting) to a particular hue: He keyed the painting to brown.</li><li>to provide with a key.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to use a key.</li></ul><p><strong>Verb Phrase</strong></p><ul><li>to single out as of prime importance or interest; be intent on or obsessed with: a company that is keyed in on growth.</li></ul>