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base 1 (bās)
1. The lowest or bottom part: the base of a cliff; the base of a lamp.
2. Biology
a. The part of a plant or animal organ that is nearest to its point of attachment.
b. The point of attachment of such an organ.
a. A supporting part or layer; a foundation: a skyscraper built on a base of solid rock.
b. A basic or underlying element; infrastructure: the nation's industrial base.
4. The fundamental principle or underlying concept of a system or theory; a basis.
5. A fundamental ingredient; a chief constituent: a paint with an oil base.
6. The fact, observation, or premise from which a reasoning process is begun.
a. Games A starting point, safety area, or goal.
b. Baseball Any one of the four corners of an infield, marked by a bag or plate, that must be touched by a runner before a run can be scored.
a. A center of organization, supply, or activity; a headquarters.
b. The portion of a social organization, especially a political party, consisting of the most dedicated or motivated members.
a. A fortified center of operations.
b. A supply center for a large force of military personnel.
10. A facial cosmetic used to even out the complexion or provide a surface for other makeup; a foundation.
11. Architecture The lowest part of a structure, such as a wall, considered as a separate unit: the base of a column.
12. Heraldry The lower part of a shield.
13. Linguistics A morpheme or morphemes regarded as a form to which affixes or other bases may be added.
14. Mathematics
a. The side or face of a geometric figure to which an altitude is or is thought to be drawn.
b. The number that is raised to various powers to generate the principal counting units of a number system. The base of the decimal system, for example, is 10.
c. The number raised to the logarithm of a designated number in order to produce that designated number; the number at which a chosen logarithmic scale has the value 1.
15. A line used as a reference for measurement or computations.
16. Chemistry
a. Any of a class of compounds whose aqueous solutions are characterized by a bitter taste, a slippery feel, the ability to turn litmus blue, and the ability to react with acids to form salts.
b. A substance that yields hydroxide ions when dissolved in water.
c. A substance that can act as a proton acceptor.
d. A substance that can donate a pair of electrons to form a covalent bond.
17. Electronics
a. The region in a transistor between the emitter and the collector.
b. The electrode attached to this region.
18. One of the nitrogen-containing purines (adenine and guanine) or pyrimidines (cytosine, thymine, and uracil) that occurs attached to the sugar component of DNA or RNA.
1. Forming or serving as a base: a base layer of soil.
2. Situated at or near the base or bottom: a base camp for the mountain climbers.
3. Chemistry Of, relating to, or containing a base.
tr.v. based, bas·ing, bas·es
1. To form or provide a base for: based the new company in Portland.
2. To find a basis for; establish: based her conclusions on the report; a film based on a best-selling novel.
3. To assign to a base; station: troops based in the Middle East.
off base
Badly mistaken.

[Middle English, from Old French, from Latin basis, from Greek; see gwā- in the Appendix of Indo-European roots.]

Synonyms: base1, basis, foundation, ground1, groundwork
These nouns all pertain to what underlies and supports. Base is used broadly in both literal and figurative contexts: the wide base of the pyramid; a party seeking to expand its power base.
Basis is used in a nonphysical sense: "Healthy scepticism is the basis of all accurate observation" (Arthur Conan Doyle).
Foundation often stresses firmness of support for something of relative magnitude: "Our flagrant disregard for the law attacks the foundation of this society" (Peter D. Relic).
Ground is used figuratively, especially in the plural, to mean a justifiable reason: grounds for divorce.
Groundwork usually has the sense of a necessary preliminary: "It [the Universal Declaration of Human Rights] has laid the groundwork for the world's war crimes tribunals" (Hillary Rodham Clinton).

The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2017 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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