part of speech

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

• noun One of a group of traditional classifications of words according to their functions in context, usually including the noun, pronoun, verb, adjective, adverb, preposition, conjunction, interjection, and article.
• noun One of a group of theoretical classifications of words according to their syntactic, morphological, and semantic properties, such as the noun, determiner, verb, adjective, adverb, complementizer, preposition, and conjunction.

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

• noun grammar A linguistic category of words sharing syntactic or morphological behaviour and semantic properties, such as noun or verb.

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

• noun one of the traditional categories of words intended to reflect their functions in a grammatical context