prolong

(verb) lengthen in time; cause to be or last longer. Synonyms: protract, extend, draw out. Examples: "We prolonged our stay." "She extended her visit by another day." "The meeting was drawn out until midnight."

(verb) lengthen or extend in duration or space. Synonyms: sustain, keep up. Examples: "We sustained the diplomatic negotiations as long as possible." "Prolong the treatment of the patient." "Keep up the good work."