algebra

noun

1. (uncountable)Elementary algebra: A system for representing and manipulating unknown quantities (variables) in equations.

   “Also the rule of false position, with dyuers examples not only vulgar, but some appertaynyng to the rule of Algeber.”

   “Let us conceive, then, of an Algebra in which the symbols x, y, z, &c. admit indifferently of the values 0 and 1, and of these values alone.”

2. (capitalized, sometimes, uncountable)Abstract algebra: A broad field of study in modern mathematics (often mentioned alongside analysis) loosely characterized by its concern for abstraction and symmetry, dealing with the behavior, classification, and application of a large class of objects (called algebraic structures) and the maps between them (called, most generally, morphisms).
3. (countable, uncountable)Any of several objects of study in Algebra
4. (countable, uncountable)Any of several objects of study in Algebra
5. (countable)A collection of subsets of a given set, such that this collection contains the empty set, and the collection is closed under unions and complements (and thereby also under intersections and differences).
6. (countable, figuratively, uncountable)A system or process (especially one that is complex or convoluted) that substitutes one thing for another, or uses signs or symbols to represent concepts or ideas.

   “Fly ! Fly ! avaunt with that base cowardly gibbrish ; That Algebra of honour ; which had never Been nam'd, if all had equal courage—what?”

7. (historical, rare, uncountable)The surgical treatment of a dislocated or fractured bone. Also (countable): a dislocation or fracture.

   “Ne take noon hede to brynge togidere þe parties of þe boon þat is to-broken or dislocate, til viij. daies ben goon in þe wyntir, & v. in þe somer; for þanne it schal make quytture, and be sikir from swellynge; & þanne brynge togidere þe brynkis eiþer þe disiuncture after þe techynge þat schal be seid in þe chapitle of algebra.”

   “Algebra is used today by surgeons to mean bone-setting, i.e. the restoration of bones, and the idea of restoration is present in the mathematical context, too.”