base¹ / bās/ • n. 1. the lowest part or edge of something, esp. the part on which it rests or is supported: she sat down at the base of a tree. ∎  Archit. the part of a column between the shaft and pedestal or pavement. ∎  Bot. & Zool. the end at which a part or organ is attached to the trunk or main part: a shoot is produced at the base of the stem. ∎  Geom. a line or surface on which a figure is regarded as standing: the base of the triangle. ∎  Surveying a line of known length used in triangulation.2. a conceptual structure or entity on which something draws or depends: the town's economic base collapsed. ∎  something used as a foundation or starting point for further work; a basis: uses existing data as the base for the study. ∎  a group of people regarded as supporting an organization, for example by buying its products: a client base.3. the main place where a person works or stays: she makes the studio her base. ∎ chiefly Mil. a place used as a center of operations by the armed forces or others; a headquarters: he headed back to base. ∎  a place from which a particular activity can be carried out: a base for shipping operations.4. a main or important element or ingredient to which other things are added: soaps with a vegetable oil base.5. Chem. a substance capable of reacting with an acid to form a salt and water, or (more broadly) of accepting or neutralizing hydrogen ions. Compare with alkali. ∎  Biochem. a purine or pyrimidine group in a nucleotide or nucleic acid.6. Electr. the middle part of a bipolar transistor, separating the emitter from the collector.7. Linguistics the root or stem of a word or a derivative. ∎  the uninflected form of a verb.8. Math. a number used as the basis of a numeration scale. ∎  a number in terms of which other numbers are expressed as logarithms.9. Baseball one of the four stations that must be reached in turn to score a run.• v. [tr.] 1. (often be based) have as the foundation for (something); use as a point from which (something) can develop: the film is based on a novel by Pat Conroy.2. situate as the center of operations: a research program based at the University of Arizona.PHRASES: get to first base inf. achieve the first step toward one's objective.first base ,second base,third base inf. used to refer to progressive levels of sexual intimacy.off-base inf. mistaken: the boy is way off-base.touch base(s) inf. briefly make or renew contact with (someone).base² • adj. (of a person or a person's actions or feelings) without moral principles; ignoble: the electorate's baser instincts of greed and selfishness. ∎  (of coins or other articles) not made of precious metal.DERIVATIVES: base·ly adv.base·ness n.