unipolar

Unipolar is an adjective meaning having a single pole or single polarity. The term, derived from Latin unus “one” and polus “pole,” is used across disciplines to describe phenomena or systems characterized by one dominant polarity or state rather than a pair or cycle of poles.

In physics and engineering, unipolar often refers to arrangements that emphasize a single polarity. For example, a unipolar (homopolar) motor or generator operates with a single polarity of current or magnetic arrangement. In electronics, unipolar transistors describe devices whose conduction is dominated by one type of charge carrier (electrons or holes), as opposed to bipolar transistors that involve both carriers.

In biology and medicine, unipolar appears in several contexts. A unipolar neuron is a sensory neuron with a single process that divides into two branches, typically described as pseudounipolar. In mood disorders, unipolar depression—also called major depressive disorder or a unipolar mood disorder—refers to mood disturbance on one end of the spectrum (depression) without the manic or hypomanic episodes seen in bipolar disorders.

In international relations, the term unipolar has been used to describe a world or regional order in which a single state exerts most of the cultural, economic, and military influence, in contrast to bipolar or multipolar systems.