complex

noun1 of 2

difficult, not easy to understand or explain

• “Science can help us understand the dynamics of complex systems.”Tatoeba
• “The biology of plants is a complex and fascinating subject.”Tatoeba

Sentences from Tatoeba show real usage. A word can have several meanings, so a sentence may use another one.

adjective2 of 2

(of a number) Having the form a + bi, where a and b are real numbers and i is (by definition) the imaginary square root of −1.