know

verb [vt. 及物动词]知道；认识到，懂得；熟悉，了解；确信，确定；把…看作是；将…称为；认出，辨认出；能区分；精通，掌握；经历，体验

If you know someone, you are familiar with them because you have met them and talked to them before.
认识•  Gifford was a friend. I'd known him for nine years. 吉福德曾是个朋友。我那时认识他已有9年。