"having two poles," from bi- + polar; 1810 with figurative sense of "of double aspect;" 1859 with reference to physiology. Psychiatric use in reference to what had been called manic-depressive psychosis is said to have begun 1957 with German psychiatrist Karl Leonhard. The term became popular early 1990s. Bipolar disorder was in DSM III (1980).
Relating to a semiconductor device, such as a transistor, that exploits the electrical characteristics of contact between two substances, one with an inherent positive charge, the other with an inherent negative charge.
Relating to or involving both of the Earth's polar regions.
Relating to a neuron that has two processes or extremities.