1. sth added to something else, an afterthought
addition to the team/project/company, make a great addition
If something is 'in addition' to something else it is added to it or 'as well as'. You might use this expression to make a point: "In addition to my previous point, I would also like to..." or to advertise an additional feature: "In addition to all of this, we also offer..." Something which is 'an addition' to something is added afterwards: "The pond was an addition to the garden." These expressions are used in both social and professional situations.