complex number

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Any number of the form a + bi, where a and b are real numbers and i is an imaginary number whose square equals -1.

Wiktionary

1. n. complex analysis A number of the form a + bi, where a and b are real numbers and i denotes the imaginary unit

GNU Webster's 1913

1. adj. (Math.) in the theory of numbers, an expression of the form a + b√-1, when a and b are ordinary integers.

WordNet 3.0

1. n. (mathematics) a number of the form a+bi where a and b are real numbers and i is the square root of -1