<p><strong>Noun</strong></p><ul><li>A secret method of writing or recording data, such as by substituting or adding letters or numbers, using specially formed symbols, or the like; code: cryptography.</li><li>The spies exchanged messages using a complex cipher.</li><li>The encryption software creates unbreakable ciphers for secure communication.</li><li>Writing, or a piece of writing, done by a secret method; a coded message: Hostile agents intercepted the cipher and began trying to figure out its meaning.</li><li>The key to a secret method of writing: After a year of studying the coded messages, the analysts were no closer to discovering the cipher.</li><li>Someone or something that is not understood; mystery or enigma: I just can’t figure him out—he’s a complete cipher to me.</li><li>Zero: a person or thing of no influence or importance; nonentity: Having lost the party leadership, she is now a mere cipher on the political scene.</li><li>Usually cypher: a performance by a group of rappers, hip-hop artists, or break dancers who take turns improvising individual verses, dances, etc.</li><li>An individual verse, dance, etc., that is part of such a performance.</li><li>Any of the Arabic numerals, such as 1, 2, or 3, or any number written with such numerals, such as 476.</li><li>Arabic numerical notation collectively: The date is MXML in Roman numerals, or 1950 in cipher.</li><li>A combination of letters, such as the initials of a name, in one design; monogram: The cipher for Queen Elizabeth II had an E entwined with an R for regina, Latin for “queen,” on either side of a Roman numeral II.</li></ul><p><strong>Verb</strong></p><ul><li>(Used with object) To pierce with or as if with a gimlet.</li><li>Also used in military contexts to instruct and exercise military trainees in formation marching and movement, in the carrying of arms during formal marching, and in the formal handling of arms for ceremonies and guard duty.</li><li>To impart (knowledge) by strict training, discipline, or repetition.</li><li>To train or rehearse (a person or group) in a subject, discipline, etc., by guided repetition, quizzing, and other techniques.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>To pierce or bore something with or as with a drill.</li><li>To penetrate deeply beneath the ground or the seafloor with specialized machinery to search for deposits or reservoirs of a natural substance: to drill for oil.</li><li>To go through exercise in military or other training.</li><li>(Computers) To move through a hierarchical system in order to view data at a lower level, as to find a specific file or database record.</li><li>To access and examine something more thoroughly or in more detail: Now that you have the big picture, let’s drill down to some technical facts and statistics.</li></ul>