<p><strong>Noun</strong></p><ul><li>Mathematics: a quantity possessing both magnitude and direction, represented by an arrow the direction of which indicates the direction of the quantity and the length of which is proportional to the magnitude; compare scalar.</li><li>Such a quantity with the additional requirement that such quantities obey the parallelogram law of addition.</li><li>Such a quantity with the additional requirement that such quantities are to transform in a particular way under changes of the coordinate system.</li><li>Any generalization of the above quantities.</li><li>The direction or course followed by an airplane, missile, or the like.</li><li>Biology: an insect or other organism that transmits a pathogenic fungus, virus, bacterium, etc.</li><li>Any agent that acts as a carrier or transporter, as a virus or plasmid that conveys a genetically engineered DNA segment into a host cell.</li><li>Computers: an array of data ordered such that individual items can be located with a single index or subscript.</li></ul><p><strong>Verb</strong></p><ul><li>(used with object) to guide (an aircraft) in flight by issuing appropriate headings; to change the direction of (the thrust of a jet or rocket engine) in order to steer the craft.</li></ul>