synonymy

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The quality of being synonymous; equivalence of meaning.
2. n. Study and classification of synonyms.
3. n. A list, book, or system of synonyms.
4. n. Biology A chronological list or record of the scientific names that have been applied to a species and its subdivisions.

Century Dictionary and Cyclopedia

1. n. The quality of being synonymous, or of expressing the same meaning by different words.
2. n. In rhetoric, a figure by which words of the same meaning are used to amplify a discourse.
3. n. A thing of the same name.
4. n. A system of synonyms; a collection of synonyms; also, the study of synonyms; the use of synonyms in expressing different shades of meaning; the discrimination of synonyms; especially, in natural history, the sifting of synonyms to determine the onyms. In botany and zoölogy the synonymy of a species of plant or animal, in the concrete, is a list of the several different names which have been applied to it by its various describers or classifiers, implying on the synonymist's part the discrimination not only of the synonyms of the species, but of the homonyms of related species, for the especial purpose of determining the onym of each species. Thus, Falco fuscus and Falco obscurus may be synonyms of one and the same species of falcon, yet Falco fuscus may be a homonym of two different species of falcon, and it may be that neither name is the onym of either of these species. Synonymy in natural history has become of late years so extensive and so intricate that probably no naturalist has mastered the subject beyond the line of some one narrow specialty. Synonymatic lists for single species extending over several pages of an ordinary book are of no infrequent occurrence. See synonym, 3.

Wiktionary

1. n. semantics The quality of being synonymous; sameness of meaning.
2. n. A list or collection of synonyms, often compared and contrasted.
3. n. The study of synonyms.
4. n. A system of synonyms.
5. n. botany The collective synonyms (all the names referring to a particular taxon, except the correct name)
6. n. botany The state of not being a correct name, of being a synonym
7. n. zoology The collective synonyms (all the names referring to the same taxon, including the correct name)

GNU Webster's 1913

1. n. The quality of being synonymous; sameness of meaning.
2. n. A system of synonyms.
3. n. (Rhet.) A figure by which synonymous words are used to amplify a discourse.

WordNet 3.0

1. n. the semantic relation that holds between two words that can (in a given context) express the same meaning