1 understand, comprehend, be familiar with, grasp, be acquainted with, be versed or skilled in:
Do you know anything about nuclear physics? I know Italian fairly well. She knows how to dance the tango
2 recognize, identify, recall, remember, recollect:
I know him from somewhere.
3 be sure or certain or positive:
I knew I was right! I just know I'm going to win the first prize.
4 distinguish, separate, discern, differentiate, recognize, identify:
Charles doesn't know right from wrong.
5 be aware or conscious or cognizant of, be informed or advised of, have knowledge of:
He knows that he cannot fire her because she knows too much.