Real Dictionary

watt
countable noun: A watt is a unit of measurement of electrical power.

Watt in American English
James1736-1819; Scot. engineer & inventor: pioneer in the development of the steam engine
the basic unit of electric, mechanical, or thermal power in the SI and MKS systems, equal to one joule per second or 107 ergs per second (1⁄746 of a horsepower): for electric power it is equal to one volt-ampere
noun: the SI unit of power, equivalent to one joule per second and equal to the power in a circuit in which a current of one ampere flows across a potential difference of one volt

Watt in British English
noun: James. 1736–1819, Scottish engineer and inventor. His fundamental improvements to the steam engine led to the widespread use of steam power in industry
noun: the derived SI unit of power, equal to 1 joule per second; the power dissipated by a current of 1 ampere flowing across a potential difference of 1 volt. 1 watt is equivalent to 1.341 × 10–3 horsepower

watt in Electrical Engineering
noun: A watt is a unit of power, equal to a power rate of one joule of work per second of time.