The tonic or first tone of the scale in which a piece or passage is written; the fundamental tone of the chord, to which all the modulations of the piece are referred; -- called also key tone. [1913 Webster]
The fundamental fact or idea; that which gives the key; as, the keynote of a policy or a sermon. [1913 Webster]

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OXFORD DICTIONARY

keynote, n.
1 a prevailing tone or idea (the keynote of the whole occasion).
2 (attrib.) intended to set the prevailing tone at a meeting or conference (keynote address).
3 Mus. the note on which a key is based.

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THESAURUS

keynote

aroma, attribute, badge, banner, be characteristic, brand, cachet, cast, character, characteristic, characterize, configuration, cut, define, demarcate, describe, device, differentia, differential, differentiate, distinctive feature, distinguish, dominant, earmark, feature, figure, flavor, gust, hallmark, idiocrasy, idiosyncrasy, image, impress, impression, index, indicant, indicator, individualism, insignia, key, key signature, lineaments, major, major key, mannerism, mark, mark off, mark out, marking, measure, mediant, minor, mold, nature, note, odor, particularity, peculiarity, pedal point, picture, property, quality, quirk, representation, representative, savor, seal, set apart, set the pace, set the tone, shape, sigil, sign, signal, signature, singularity, smack, sound the keynote, specialty, stamp, subdominant, submediant, subtonic, supertonic, sure sign, symptom, taint, tang, taste, telltale sign, token, tonality, tonic, tonic key, trait, trick

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ROGET THESAURUS

keynote

Importance

N importance, consequence, moment, prominence, consideration, mark, materialness, import, significance, concern, emphasis, interest, greatness, superiority, notability, weight, value, usefulness, gravity, seriousness, solemnity, no joke, no laughing matter, pressure, urgency, stress, matter of life and death, memorabilia, notabilia, great doings, red-letter day, great thing, great point, main chance, the be all and the end all, cardinal point, substance, gist, sum and substance, gravamen, head and front, important part, principal part, prominent part, essential part, half the battle, sine qua non, breath of one's nostrils, cream, salt, core, kernel, heart, nucleus, keynote, keystone, corner stone, trump card, salient points, top sawyer, first fiddle, prima donna, chief, triton among the minnows, 'it', important, of importance, momentous, material, to the point, not to be overlooked, not to be despised, not to be sneezed at, egregious, weighty, of note, notable, prominent, salient, signal, memorable, remarkable, unforgettable, worthy of remark, worthy of notice, never to be forgotten, stirring, eventful, grave, serious, earnest, noble, grand, solemn, impressive, commanding, imposing, urgent, pressing, critical, instant, paramount, essential, vital, all-absorbing, radical, cardinal, chief, main, prime, primary, principal, leading, capital, foremost, overruling, of vital importance in the front rank, first-rate, superior, considerable, marked, rare, significant, telling, trenchant, emphatic, pregnant, tanti, materially, in the main, above all, kat' exochin, par excellence, to crown all, to beat all, expende Hannibalem!.

Prototype

N prototype, original, model, pattern, precedent, standard, ideal, reference, scantling, type, archetype, antitype, protoplast, module, exemplar, example, ensample, paradigm, lay-figure, text, copy, design, fugleman, keynote, die, mold, matrix, last, plasm, proplasm, protoplasm, mint, seal, punch, intaglio, negative, stamp, a precedent embalms a principle, exempla sunt odiosa.

Frequency

N frequency, oftness, oftenness, commonness, repetition, normality, example (conformity), routine, custom (habit), regularity, uniformity, constancy, clock-work precision, punctuality, even tenor, system, routine, formula, rule, keynote, standard, model, precedent, conformity, frequent, many times, not rare, thickcoming, incessant, perpetual, continual, steady, constant, thick, uniform, repeated, customary, (habit), regular (normal), according to rule, common, everyday, usual, ordinary, familiar, old-hat, boring, well-known, trivial, often, oft, ofttimes, oftentimes, frequently, repeatedly, unseldom, not unfrequently, in quick succession, in rapid succession, many a time and oft, daily, hourly, every day, every hour, every moment, perpetually, continually, constantly, incessantly, without ceasing, at all times, daily and hourly, night and day, day and night, day after day, morning noon and night, ever anon, invariably (habit), most often, commonly, sometimes, occasionally, at times, now and then, from time to time, there being times when, toties quoties, often enough, when the mood strikes, again and again.

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