grammar

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

• noun The study of how words and their component parts combine to form sentences.
• noun The study of structural relationships in language or in a language, sometimes including pronunciation, meaning, and linguistic history.
• noun The system of inflections, syntax, and word formation of a language.
• noun The system of rules implicit in a language, viewed as a mechanism for generating all sentences possible in that language.
• noun A normative or prescriptive set of rules setting forth the current standard of usage for pedagogical or reference purposes.
• noun Writing or speech judged with regard to such a set of rules.
• noun A book containing the morphologic, syntactic, and semantic rules for a specific language.
• noun The basic principles of an area of knowledge.
• noun A book dealing with such principles.

from The Century Dictionary.

• To discourse according to the rules of grammar.
• noun A systematic account of the usages of a language, as regards especially the parts of speech it distinguishes, the forms and uses of inflected words, and the combinations of words into sentences; hence, also, a similar account of a group of languages, or of all languages or language in general, so far as these admit a common treatment.
• noun Grammatical statements viewed as the rules of a language to which speakers or writers must conform; propriety of linguistic usage; accepted or correct mode of speech or writing.
• noun A treatise on grammar.
• noun An account of the elements of any branch of knowledge, prepared for teaching or learning: an outline or sketch of the principles of a subject: as, a grammar of geography; a grammar of art.
• noun The formal principles of any science; a system of rules to be observed in the putting together of any kind of elements.

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

• intransitive verb obsolete To discourse according to the rules of grammar; to use grammar.
• noun The science which treats of the principles of language; the study of forms of speech, and their relations to one another; the art concerned with the right use and application of the rules of a language, in speaking or writing.
• noun The art of speaking or writing with correctness or according to established usage; speech considered with regard to the rules of a grammar.
• noun A treatise on the principles of language; a book containing the principles and rules for correctness in speaking or writing.
• noun treatise on the elements or principles of any science.
• noun the science which determines the relations of kindred languages by examining and comparing their grammatical forms.
• noun A school, usually endowed, in which Latin and Greek grammar are taught, as also other studies preparatory to colleges or universities; as, the famous Rugby Grammar School. This use of the word is more common in England than in the United States.

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

• noun A system of rules and principles for speaking and writing a language.
• noun uncountable, linguistics The study of the internal structure of words (morphology) and the use of words in the construction of phrases and sentences (syntax).
• noun A book describing the rules of grammar of a language.
• noun computing theory A formal system specifying the syntax of a language.
• noun computing theory A formal system defining a formal language
• noun The basic rules or principles of a field of knowledge or a particular skill.
• noun UK, archaic a textbook.
• noun UK A grammar school.
• verb obsolete, intransitive To discourse according to the rules of grammar; to use grammar.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)