grammar

American Heritage® Dictionary of the English Language, Fourth Edition

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

Century Dictionary and Cyclopedia

1. n. 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. The formerly current classification of the subjects of grammar as fivefold, namely, orthography, orthoëpy, etymology, syntax, and prosody, is heterogeneous and obsolescent. The first and last do not belong really to grammar, though often for convenience included in the text-books of grammar; orthoëpy is properly phonology or phonetics, an account of the system of sounds used by a language and of their combinations; and etymology is improperly used for an account of the parts of speech and their inflections. See these words. Abbreviated grammar
2. n. 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.
3. n. A treatise on grammar.
4. n. 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.
5. n. The formal principles of any science; a system of rules to be observed in the putting together of any kind of elements.
6. To discourse according to the rules of grammar.

Wiktionary

1. n. A system of rules and principles for speaking and writing a language.
2. n. The study of the internal structure of words (morphology) and the use of words in the construction of phrases and sentences (syntax).
3. n. A book describing the rules of grammar of a language.
4. n. A formal system specifying the syntax of a language.
5. n. A formal system defining a formal language
6. n. a textbook.

GNU Webster's 1913

1. n. 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.
2. n. The art of speaking or writing with correctness or according to established usage; speech considered with regard to the rules of a grammar.
3. n. A treatise on the principles of language; a book containing the principles and rules for correctness in speaking or writing.
4. n. treatise on the elements or principles of any science.
5. v. To discourse according to the rules of grammar; to use grammar.

WordNet 3.0

1. n. the branch of linguistics that deals with syntax and morphology (and sometimes also deals with semantics)