The Collaborative International Dictionary
magnetic monopole \magnetic monopole\ (Physics), a hypothetical subatomic particle having only one type of magnetic charge, the magnetic analogue of an electrically charged particle; it has only one magnetic pole instead of the two observed in all common magnetic object; -- it was still not observed as of 1998.
Wiktionary
n. (context physics English) a hypothetical particle having an isolated north pole or south pole; the magnetic equivalent of an isolated electric charge
WordNet
n. a hypothetical particle with a single magnetic pole instead of the usual two
Wikipedia
A magnetic monopole is a hypothetical elementary particle in particle physics that is an isolated magnet with only one magnetic pole (a north pole without a south pole or vice versa). In more technical terms, a magnetic monopole would have a net "magnetic charge". Modern interest in the concept stems from particle theories, notably the grand unified and superstring theories, which predict their existence.
Magnetism in bar magnets and electromagnets does not arise from magnetic monopoles. There is no experimental evidence that magnetic monopoles exist.
Some condensed matter systems contain effective (non-isolated) magnetic monopole quasi-particles, or contain phenomena that are mathematically analogous to magnetic monopoles.
Usage examples of "magnetic monopole".
And a magnetic monopole detector, orbiting the sun out of the plane of the ecliptic, had captured a trace of what looked to be a fractionally charged unconfined particle with a mass as big as a bacterium—.