pro·long 
(prə-lông, -lŏng)
(prə-lông, -lŏng)tr.v. pro·longed, pro·long·ing, pro·longs
To lengthen in duration; protract: factors that prolong the drug's effect.
[Middle English prolongen, from Old French prolonguer, from Late Latin prōlongāre : Latin prō-, forth; see PRO-1 + Latin longus, long; see del-1 in the Appendix of Indo-European roots.]
pro·longer n.