add by mixing or blending on or attaching; "work in the butter and the dough will get the right consistency"; "In his speech, the presidential candidate worked in a lot of learned words"
lengthen in time; cause to be or last longer; "We prolonged our stay"; "She extended her visit by another day"; "The meeting was drawn out until midnight"
lengthen or extend in duration or space; "We sustained the diplomatic negotiations as long as possible"; "prolong the treatment of the patient"; "keep up the good work"