topic

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

• noun The subject of a speech, essay, thesis, or discourse.
• noun A subject of discussion or conversation.
• noun A subdivision of a theme, thesis, or outline. synonym: subject.
• noun Linguistics A word or phrase in a sentence, usually providing information from previous discourse or shared knowledge, that the rest of the sentence elaborates or comments on.

from The Century Dictionary.

• Local: same as topical.
• noun In logic and rhetoric, a common place (which see, under common); a class of considerations from which probable arguments can be drawn.
• noun The subject of a discourse, argument, or literary composition, or the subject of any distinct part of a discourse, etc.; any matter treated of: now the usual meaning of the word.
• noun In medicine, a remedy locally applied.
• noun Synonyms Theme, Point, etc. See subject.
• noun plural In geometry, topology. See topics, 2.

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

• adjective Topical.
• noun One of the various general forms of argument employed in probable as distinguished from demonstrative reasoning, -- denominated by Aristotle to`poi (literally, places), as being the places or sources from which arguments may be derived, or to which they may be referred; also, a prepared form of argument, applicable to a great variety of cases, with a supply of which the ancient rhetoricians and orators provided themselves; a commonplace of argument or oratory.
• noun A treatise on forms of argument; a system or scheme of forms or commonplaces of argument or oratory.
• noun obsolete An argument or reason.
• noun The subject of any distinct portion of a discourse, or argument, or literary composition; also, the general or main subject of the whole; a matter treated of; a subject, as of conversation or of thought; a matter; a point; a head.
• noun (Med.), obsolescent An external local application or remedy, as a plaster, a blister, etc.

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

• adjective topical
• noun Subject; theme; a category or general area of interest.
• noun Internet discussion thread

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

• noun the subject matter of a conversation or discussion
• noun some situation or event that is thought about