1. of the first importance; demanding the fullest consideration: a prime requisite.
  2. of the greatest relevance or significance: a prime example.
  3. of the highest eminence or rank: the prime authority on Chaucer.
  4. of the greatest commercial value: prime building lots.
  5. first-rate: This ale is prime!
  6. (of meat, especially of beef) noting or pertaining to the first grade or best quality: prime ribs of beef.
  7. first in order of time, existence, or development; earliest; primitive.
  8. basic; fundamental: the prime axioms of his philosophy.
  9. Mathematics. (of any two or more numbers) having no common divisor except unity: The number 2 is prime to 9.


  1. the most flourishing stage or state.
  2. the time of early manhood or womanhood: the prime of youth.
  3. the period or state of greatest perfection or vigor of human life: a man in his prime.
  4. the choicest or best part of anything.
  5. (especially in the grading of U.S. beef) a grade, classification, or designation indicating the highest or most desirable quality.
  6. the beginning or earliest stage of any period.
  7. the spring of the year.
  8. the first hour or period of the day, after sunrise.
  9. Banking. prime rate.
  10. Ecclesiastical. the second of the seven canonical hours or the service for it, originally fixed for the first hour of the day.
  11. Mathematics.
    1. prime number.
    2. one of the equal parts into which a unit is primarily divided.
    3. the mark (′) indicating such a division: a, a′.
  12. Fencing. the first of eight defensive positions.
  13. Music.
    1. unison(def 2).
    2. (in a scale) the tonic or keynote.
  14. Linguistics. any basic, indivisible unit used in linguistic analysis.
  15. Metallurgy. a piece of tin plate free from visible defects.

verb (used with object), primed, prim·ing.

  1. to prepare or make ready for a particular purpose or operation.
  2. to supply (a firearm) with powder for communicating fire to a charge.
  3. to lay a train of powder to (a charge, mine, etc.).
  4. to pour or admit liquid into (a pump) to expel air and prepare for action.
  5. to put fuel into (a carburetor) before starting an engine, in order to insure a sufficiently rich mixture at the start.
  6. to cover (a surface) with a preparatory coat or color, as in painting.
  7. to supply or equip with information, words, etc., for use: The politician was primed by his aides for the press conference.
  8. to harvest the bottom leaves from (a tobacco plant).

verb (used without object), primed, prim·ing.

  1. (of a boiler) to deliver or discharge steam containing an excessive amount of water.
  2. to harvest the bottom leaves from a tobacco plant.


  1. (prenominal) first in quality or value; first-rate
  2. (prenominal) fundamental; original
  3. (prenominal) first in importance, authority, etc; chief
  4. maths
    1. having no factors except itself or onex² + x + 3 is a prime polynomial
    2. (foll by to)having no common factors (with)20 is prime to 21
  5. finance having the best credit ratingprime investments


  1. the time when a thing is at its best
  2. a period of power, vigour, etc, usually following youth (esp in the phrase the prime of life)
  3. the beginning of something, such as the spring
  4. maths short for prime number
  5. linguistics a semantically indivisible element; minimal component of the sense of a word
  6. music
    1. unison
    2. the tonic of a scale
  7. mainly RC Church the second of the seven canonical hours of the divine office, originally fixed for the first hour of the day, at sunrise
  8. the first of eight basic positions from which a parry or attack can be made in fencing


  1. to prepare (something); make ready
  2. (tr) to apply a primer, such as paint or size, to (a surface)
  3. (tr) to fill (a pump) with its working fluid before starting, in order to improve the sealing of the pump elements and to expel air from it before starting
  4. (tr) to increase the quantity of fuel in the float chamber of (a carburettor) in order to facilitate the starting of an engine
  5. (tr) to insert a primer into (a gun, mine, charge, etc) preparatory to detonation or firing
  6. (intr) (of a steam engine or boiler) to operate with or produce steam mixed with large amounts of water
  7. (tr) to provide with facts, information, etc, beforehand; brief

late 14c., “first in order,” from Latin primus “first, the first, first part,” figuratively “chief, principal; excellent, distinguished, noble” (source also of Italian and Spanish primo), from pre-Italic *prismos, superlative of PIE *preis- “before,” from root *per- (1) “beyond, through” (see per).

Meaning “first in importance” is from 1610s in English; that of “first-rate” is from 1620s. Arithmetical sense (e.g. prime number) is from 1560s; prime meridian is from 1878. Prime time originally (c.1500) meant “spring time;” broadcasting sense of “peak tuning-in period” is attested from 1961.


“earliest canonical hour” (6 a.m.), Old English prim, from Medieval Latin prima “the first service,” from Latin prima hora “the first hour” (of the Roman day). Meaning “most vigorous stage” first recorded 1530s; specifically “springtime of human life” (often meaning ages roughly 21 to 28) is from 1590s. In classical Latin, noun uses of the adjective meant “first part, beginning; leading place.”


“to fill, charge, load” (a weapon), 1510s, probably from prime (adj.). Meaning “to cover with a first coat of paint or dye” is from c.1600. To prime a pump (c.1840) meant to pour water down the tube, which saturated the sucking mechanism and made it draw up water more readily. Related: Primed; priming.

In addition to the idioms beginning with prime

  • prime mover
  • prime of life
  • prime the pump

also see:

  • past one’s prime
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