Used as a response meaning fairly good or well, to questions such as “How are you?” or “How is business?” For example, How've you been?—Can't complain. This term means that nothing serious is wrong. [Mid-1800s]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.