comma

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

• noun Grammar A punctuation mark ( , ) used to indicate a separation of ideas or of elements within the structure of a sentence.
• noun A pause or separation; a caesura.
• noun Any of several nymphalid butterflies of the genus Polygonia having wings with irregularly notched edges and a small comma-shaped marking on the underside of the hind wing.

from The Century Dictionary.

• noun In ancient Grammar and rhetoric, a group of a few words only; a phrase or short clause, forming part of a colon or longer clause.
• noun In ancient prosody: A fragment or smaller section of a colon; a group of a few words or feet not constituting a complete metrical series.
• noun The part of a dactylic hexameter ending with, or that beginning with, the cesura; also, the cesura itself.
• noun A clause.
• noun In rhetoric, a slight pause between two phrases, clauses, or words.
• noun In musical acoustics: The interval between the octave of a given tone and the tone produced by taking six successive whole steps from the given tone, represented by the ratios , or 531441:524288. Also called the Pythagorean comma, or comma maxima.
• noun The interval between the larger and the smaller whole steps, represented by the ratio , or 81:80. Also called the Didymic or syntonic comma.
• noun In punctuation, a point (,) used to indicate the smallest interruptions in continuity of thought or grammatical construction, the marking of which contributes to clearness.
• noun A spot or mark shaped like such a comma.
• noun In entomology: A butterfly, Grapta comma-album: so named from a comma-shaped white mark on the under side of the wings.
• noun [capitalized] [NL.] A genus of lepidopterous insects.

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

• noun A character or point [,] marking the smallest divisions of a sentence, written or printed.
• noun (Mus.) A small interval (the difference between a major and minor half step), seldom used except by tuners.
• noun (Physiol.) a variety of bacillus shaped like a comma, found in the intestines of patients suffering from cholera. It is considered by some as having a special relation to the disease; -- called also cholera bacillus.
• noun (Zoöl.) an American butterfly (Grapta comma), having a white comma-shaped marking on the under side of the wings.

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

• noun Punctuation mark (,) (usually indicating a pause between parts of a sentence or between elements in a list).
• noun by extension A diacritical mark used below certain letters in Romanian.
• noun A European and North American butterfly, Polygonia c-album, of the family Nymphalidae.
• noun music a small or very small interval between two enharmonic notes tuned in different ways.

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

• noun a punctuation mark (,) used to indicate the separation of elements within the grammatical structure of a sentence
• noun anglewing butterfly with a comma-shaped mark on the underside of each hind wing