Longman Dictionary of Contemporary English
Douglas Harper's Etymology Dictionary
alt. The wearing of clothing which society considers appropriate for the opposite sex. n. The wearing of clothing which society considers appropriate for the opposite sex. vb. (present participle of cross-dress English)
Cross-dressing is the act of wearing items of clothing and other accoutrements commonly associated with the opposite sex within a particular society. Cross-dressing has been used for purposes of disguise, comfort, and self-actualization in modern times and throughout history.
Almost every human society throughout history has had expected norms for each gender relating to style, color, or type of clothing they are expected to wear, and likewise most societies have had a set of guidelines, views or even laws defining what type of clothing is appropriate for each gender.
The term cross-dressing denotes an action or a behavior without attributing or implying any specific causes for that behavior. It is often assumed that the connotation is directly correlated with behaviors of transgender identity or sexual, fetishist, and homosexual behavior, but the term itself does not imply any motives and is not synonymous to one's gender identity.