Merriam-Webster Collegiate Dictionary - key

 I. noun  Etymology: Middle English, from Old English c?g; akin to Old Frisian kei ~  Date: before 12th century  1.  a. a usually metal instrument by which the bolt of a lock is turned  b. any of various devices having the form or function of such a ~  2.  a. a means of gaining or preventing entrance, possession, or control  b. an instrumental or deciding factor  3.  a. something that gives an explanation or identification or provides a solution the ~ to a riddle  b. a list of words or phrases giving an explanation of symbols or abbreviations  c. an aid to interpretation or identification ; clue  d. an arrangement of the salient characters of a group of plants or animals or of taxa designed to facilitate identification  e. a map legend  4.  a.  (1) cotter pin  (2) cotter  b. a ~stone in an arch  c. a small piece of wood or metal used as a wedge or for preventing motion between parts  5.  a. one of the levers of a ~board musical instrument that actuates the mechanism and produces the tones  b. a lever that controls a vent in the side of a woodwind instrument or a valve in a brass instrument  c. a part to be depressed by a finger that serves as one unit of a ~board  6. samara  7. a system of tones and harmonies generated from a hierarchical scale of seven tones based on a tonic the ~ of G major  8.  a. characteristic style or tone  b. the tone or pitch of a voice  c. the predominant tone of a photograph with respect to its lightness or darkness  9. a decoration or charm resembling a ~  10. a small switch for opening or closing an electric circuit a telegraph ~  11. the set of instructions governing the encipherment and decipherment of messages  12. a free-throw area in basketball  • ~ed adjective  • ~less adjective  II. verb  Date: 14th century  transitive verb  1. to lock with or as if with a ~ ; fasten: as  a. to secure (as a pulley on a shaft) by a ~  b. to finish off (an arch) by inserting a ~stone  2. to regulate the musical pitch of  3. to bring into harmony or conformity ; make appropriate ; attune remarks ~ed to a situation  4. to identify (a biological specimen) by a ~  5. to provide with identifying or explanatory cross-references instructions ~ed to accompanying drawings — John Gartner  6. to make nervous, tense, or excited — usually used with up was ~ed up over her impending operation  7. ~board — often used with in  8. to be essential to ; play the most important part in defense ~ed the victory  intransitive verb  1. to use a ~  2. to observe the position or movement of an opposing player in football in order to anticipate the play — usually used with on  3. ~board  III. adjective  Date: 1913 important, fundamental ~ issues  IV. noun  Etymology: Spanish cayo, from Taino  Date: 1697 a low island or reef; specifically any of the coral islets off the southern coast of Florida  V. noun  Etymology: by shortening & alteration from kilo  Date: 1968 slang a kilogram especially of marijuana or heroin KEY  biographical name Francis Scott 1779-1843 American lawyer & author of “The Star-Spangled Banner”