No wonder definitions are confusing. Even the dictionaries can't agree. Gender used to always refer to grammar, not biology. Since the 1960's, people started using "gender" as a substitute (incorrectly) for "sex."
gender [jen-der]
noun
1.Grammar.
a.(in many languages) a set of classes that together include all nouns, membership in a particular class being shown by the form of the noun itself or by the form or choice of words that modify, replace, or otherwise refer to the noun, as, in English, the choice of he to replace the man, of she to replace the woman, of it to replace the table, of it or she to replace the ship. The number of genders in different languages varies from 2 to more than 20; often the classification correlates in part with sex or animateness. The most familiar sets of genders are of three classes (as masculine, feminine, and neuter in Latin and German) or of two (as common and neuter in Dutch, or masculine and feminine in French and Spanish).
b.one class of such a set.
c.such classes or sets collectively or in general.
d.membership of a word or grammatical form, or an inflectional form showing membership, in such a class.
2.sex: the feminine gender.
3.Archaic. kind, sort, or class.
Origin: 1300–50; Middle English < Middle French gendre, genre < Latin gener- (stem of genus) kind, sort
gender (ˈdʒɛndə)
—n
1. See also natural gender a set of two or more grammatical categories into which the nouns of certain languages are divided, sometimes but not necessarily corresponding to the sex of the referent when animate
2. any of the categories, such as masculine, feminine, neuter, or common, within such a set
3. informal the state of being male, female, or neuter
4. informal all the members of one sex: the female gender
[C14: from Old French gendre, from Latin genus kind]
Collins English Dictionary - Complete & Unabridged 10th Edition
2009 © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009
gender
c.1300, from O.Fr. gendre, from stem of L. genus (gen. generis) "kind, sort, gender," also "sex" (see genus); used to translate from Gk. Aristotle's grammatical term genos. As sex took on erotic qualities in 20c., gender came to be used for "sex of a human being," often in feminist writing with reference to social attributes as much as biological qualities; this sense first attested 1963.
Online Etymology Dictionary, © 2010 Douglas Harper
gen·der definition
Pronunciation: /ˈjen-dər/ Function: n
1 : SEX 12 : the behavioral, cultural, or psychological traits typically associated with one sex
Merriam-Webster's Medical Dictionary, © 2007 Merriam-Webster, Inc.
gender gen·der (jěn'dər) n.
The sex of an individual, male or female, based on reproductive anatomy.
Sexual identity, especially in relation to society or culture.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
gender definition
A grammatical category indicating the sex, or lack of sex, of nouns and pronouns. The three genders are masculine, feminine, and neuter. He is a masculine pronoun; she is a feminine pronoun; it is a neuter pronoun. Nouns are classified by gender according to the gender of the pronoun that can substitute for them. In English, gender is directly indicated only by pronouns.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.