bisexual

First recorded in 1815–25; bi-¹ + sexual

Bisexual is sometimes interpreted to mean romantic, emotional, or sexual attraction to exactly two genders, often but not always men and women. However, since at least the 1990s, many bisexual people have been using definitions that acknowledge attraction to more than two genders, including people who do not fit into the gender binary. For some speakers, the bi- in bisexual refers to a gender or genders that are the same as or similar to their own, and a gender or genders that are different from their own. For others, the bi- in bisexual is simply an etymological quirk, like the octo- in October, which is no longer the eighth month.
The debate over the definition of bi- also extends to related labels such as pansexual and omnisexual. Pansexual, for example, is sometimes defined as attraction regardless of gender, and omnisexual as attraction to any gender but not regardless of gender. However, bisexual, pansexual, and omnisexual can all be accurately used to describe a person who is attracted to men, women, and other genders, and some speakers use these words interchangeably. Many factors may be involved in a person's choice of which label to use for their sexuality.

As with many other labels used to describe people, the adjective form ( a bisexual author ) is preferred over the noun form. The noun, while sometimes acceptable in the plural (a flag designed for bisexuals ), is often less acceptable in the singular ( a bisexual I work with), especially when not used for self-reference.