of the first importance; demanding the fullest consideration: a prime requisite.
of the greatest relevance or significance: a prime example.
of the highest eminence or rank: the prime authority on Chaucer.
of the greatest commercial value: prime building lots.
first-rate: This ale is prime!
(of meat, especially of beef) noting or pertaining to the first grade or best quality: prime ribs of beef.
first in order of time, existence, or development; earliest; primitive.
basic; fundamental: the prime axioms of his philosophy.
Mathematics. (of any two or more numbers) having no common divisor except unity: The number 2 is prime to 9.
the most flourishing stage or state.
the time of early manhood or womanhood: the prime of youth.
the period or state of greatest perfection or vigor of human life: a man in his prime.
the choicest or best part of anything.
(especially in the grading of U.S. beef) a grade, classification, or designation indicating the highest or most desirable quality.
the beginning or earliest stage of any period.
the spring of the year.
the first hour or period of the day, after sunrise.
Banking. prime rate.
Ecclesiastical. the second of the seven canonical hours or the service for it, originally fixed for the first hour of the day.
one of the equal parts into which a unit is primarily divided.
the mark (′) indicating such a division: a, a′.
Fencing. the first of eight defensive positions.
unison ( def 2 ).
(in a scale) the tonic or keynote.
Linguistics. any basic, indivisible unit used in linguistic analysis.
Metallurgy. a piece of tin plate free from visible defects.
verb (used with object), primed, priming.
to prepare or make ready for a particular purpose or operation.
to supply (a firearm) with powder for communicating fire to a charge.
to lay a train of powder to (a charge, mine, etc.).
to pour or admit liquid into (a pump) to expel air and prepare for action.
to put fuel into (a carburetor) before starting an engine, in order to insure a sufficiently rich mixture at the start.
to cover (a surface) with a preparatory coat or color, as in painting.
to supply or equip with information, words, etc., for use: The politician was primed by his aides for the press conference.
to harvest the bottom leaves from (a tobacco plant).
verb (used without object), primed, priming.
(of a boiler) to deliver or discharge steam containing an excessive amount of water.
to harvest the bottom leaves from a tobacco plant.

before 1000; 1910–15 for def 5; (adj.) Middle English (< Old French prim) < Latin prīmus first (superlative corresponding to prior prior1); (noun) in part derivative of the adj.; in part continuing Middle English prim(e) first canonical hour, Old English prim < Latin prīma (hōra) first (hour); (v.) apparently derivative of the adj.

primeness, noun
nonprime, adjective
reprime, verb (used with object), reprimed, repriming.
self-primed, adjective
unprimed, adjective
well-primed, adjective

1. primary. 7. Prime, primeval, primitive have reference to that which is first. Prime means first in numerical order or order of development: prime meridian; prime cause. Primeval means belonging to the first or earliest ages: the primeval forest. Primitive suggests the characteristics of the origins or early stages of a development, and hence implies the simplicity of original things: primitive tribes, conditions, ornaments, customs, tools. Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
prime (praɪm)
1.  (prenominal) first in quality or value; first-rate
2.  (prenominal) fundamental; original
3.  (prenominal) first in importance, authority, etc; chief
4.  maths
 a.  having no factors except itself or one: x² + x + 3 is a prime polynomial
 b.  (foll by to) having no common factors (with): 20 is prime to 21
5.  finance having the best credit rating: prime investments
6.  the time when a thing is at its best
7.  a period of power, vigour, etc, usually following youth (esp in the phrase the prime of life)
8.  the beginning of something, such as the spring
9.  maths short for prime number
10.  linguistics a semantically indivisible element; minimal component of the sense of a word
11.  music
 a.  unison
 b.  the tonic of a scale
12.  chiefly RC Church the second of the seven canonical hours of the divine office, originally fixed for the first hour of the day, at sunrise
13.  the first of eight basic positions from which a parry or attack can be made in fencing
14.  to prepare (something); make ready
15.  (tr) to apply a primer, such as paint or size, to (a surface)
16.  (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
17.  (tr) to increase the quantity of fuel in the float chamber of (a carburettor) in order to facilitate the starting of an engine
18.  (tr) to insert a primer into (a gun, mine, charge, etc) preparatory to detonation or firing
19.  (intr) (of a steam engine or boiler) to operate with or produce steam mixed with large amounts of water
20.  (tr) to provide with facts, information, etc, beforehand; brief
[(adj) C14: from Latin prīmus first; (n) C13: from Latin prīma (hora) the first (hour); (vb) C16: of uncertain origin, probably connected with n]

Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
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Word Origin & History

1399, from L. primus "first," from pre-Italic *prismos, superl. of Old L. pri "before," from PIE base *per- "beyond," *pro- "before" (see pre-). 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. Arithmetical sense (prime number) is from 1570; prime meridian is from 1878. Priming "first coat of paint" is from 1609. Prime time originally (1503) meant "spring time;" broadcasting sense of "peak tuning-in period" is attested from 1964.

O.E. prim "earliest canonical hour" (6 a.m.), from M.L. prima "the first service," from L. prima hora "the first hour" (of the Roman day). Meaning "most vigorous stage" first recorded 1536; specifically "springtime of human life" (often meaning ages roughly 21 to 28) is from 1592.

"to fill, charge, load" (a weapon), 1513, probably from prime (adj.) (q.v.). Primer "explosive cap" is from 1819.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Idioms & Phrases


In addition to the idioms beginning with prime, also see past one's prime.

The American Heritage® Dictionary of Idioms by Christine Ammer.
Copyright © 1997. Published by Houghton Mifflin.
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Example sentences
Summer is the prime time to make this drive, though spring and fall can also be
The answer to that question is prime pop culture trivia.
Casting about for prime numbers might seem like an odd avocation, but there's a
  financial incentive for skilled mathematicians.
This ecoregion is also a prime spot for migrating birds.
Idioms & Phrases
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