When you read the last few pages of a good book very slowly so you can enjoy reading it longer, this is an example of a time when you prolong the book.
Origin of prolongMiddle English prolongen ; from Middle French prolonguer ; from Late Latin prolongare ; from Classical Latin pro-, forth + longus, long: see pro- and amp; long
transitive verbpro·longed, pro·long·ing, pro·longs
Origin of prolongMiddle English prolongen, from Old French prolonguer, from Late Latin prōlongāre : Latin prō-, forth; see pro–1 + Latin longus, long; see del-1 in Indo-European roots.
(third-person singular simple present prolongs, present participle prolonging, simple past and past participle prolonged)