antonym means that complex will be the opposite of "simple"--and the opposite of something simple is something difficult, or something with a lot of interconnected parts.
a visual example would be that simple is from point A to point B. easy. a straight line across.
then complex is from point A to point C, then to point D, then back to point A, maybe even stopping by point E. the line looks tangled and it's more difficult to trace, or understand. that's complex.
