class

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A set, collection, group, or configuration containing members regarded as having certain attributes or traits in common; a kind or category.
• noun A division based on quality, rank, or grade, as.
• noun A grade of mail.
• noun A quality of accommodation on public transport.
• noun A social stratum whose members share certain economic, social, or cultural characteristics.
• noun Social rank or caste, especially high rank.
• noun Informal Elegance of style, taste, and manner.
• noun A group of students who are taught together, usually at a regularly scheduled time and in the same subject.
• noun The period during which such a group meets.
• noun The subject material taught to or studied by such a group.
• noun A group of students or alumni who have the same year of graduation.
• noun Biology A taxonomic category ranking below a phylum or division and above an order.
• noun Statistics An interval in a frequency distribution.
• noun Linguistics A group of words belonging to the same grammatical category that share a particular set of morphological properties, such as a set of inflections.
• noun Mathematics A collection of sets whose members share a specified property.
• transitive verb To arrange, group, or rate according to qualities or characteristics; assign to a class; classify.

from The Century Dictionary.

• In shipbuilding, to assign to a class of a registration society, such as Lloyd's: said of a merchant vessel. A vessel not classed is one which has not been inspected and assigned a class by any registration society, or the classification of which has been refused for some reason, not necessarily involving deterioration or inferior quality.
• To be assigned to a class. See I., 3.
• An abbreviation of classic or classical
• of classification.
• noun In anc. hist., one of the five divisions of the Roman citizens made, according to their wealth, by Servius Tullius, for purposes of taxation: a sixth division comprised those whose possessions fell below the minimum of the census.
• noun An order or rank of persons; a number of persons having certain characteristics in common, as equality in rank, intellectual influence, education, property, occupation, habits of life, etc.
• noun Any body of persons grouped together by particular circumstances or for particular reasons.
• noun A number of objects distinguished by common characters from all others, and regarded as a collective unit or group; a collection capable of a general definition; a kind.
• noun In natural history, a group of plants or animals next in rank above the order or superorder, and commonly formed by the union of several orders or superorders: but it may be represented by a single species. See classification.
• noun In geometry, the degree of a locus of planes; a division of algebraical loci bearing an ordinal number showing how many planes there are incident to the locus and passing through each line of Space.
• To arrange in a class or classes; rank together; regard as constituting a class; refer to a class or group; classify; range.
• To place in ranks or divisions, as students that are pursuing the same studies; form into a class or classes, as in an educational institution.
• To be arranged or classed.
• noun In petrography, in the quantitative classification of igneous rocks (see rock), the highest division.
• noun In shipbuilding, the indication of the character, style of construction, and quality of workmanship and outfit of a merchant vessel, as determined by the rules and inspection of a registration society. The class to which a vessel is assigned is indicated in the register of each society by a conventional character such as 100A, 90A, etc. See A, 2 .
• noun the indication of the size and power of any given type of war-ship: as, a first-class battle-ship, a first-, second-, or third-class cruiser, etc.
• noun In crystallog., one of the thirty-two groups in which crystals are divided in accordance with the special type of symmetry which characterizes them. See symmetry.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To be grouped or classed.
• adjective informal exhibiting refinement and high character. Opposite of low-class
• transitive verb To arrange in classes; to classify or refer to some class.
• transitive verb To divide into classes, as students; to form into, or place in, a class or classes.
• noun A group of individuals ranked together as possessing common characteristics.
• noun A number of students in a school or college, of the same standing, or pursuing the same studies.
• noun A comprehensive division of animate or inanimate objects, grouped together on account of their common characteristics, in any classification in natural science, and subdivided into orders, families, tribes, genera, etc.
• noun A set; a kind or description, species or variety.
• noun (Methodist Church) One of the sections into which a church or congregation is divided, and which is under the supervision of a class leader.
• noun One session of formal instruction in which one or more teachers instruct a group on some subject. The class may be one of a course of classes, or a single special session.
• noun A high degree of elegance, in dress or behavior; the quality of bearing oneself with dignity, grace, and social adeptness.
• noun (Math.) the kind of a curve as expressed by the number of tangents that can be drawn from any point to the curve. A circle is of the second class.
• noun (Methodist Church) a meeting of a class under the charge of a class leader, for counsel and relegious instruction.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun countable A group, collection, category or set sharing characteristics or attributes.