improvise

verb

1. To make something up or invent it as one goes on; to proceed guided only by imagination, intuition, and guesswork rather than by a careful plan.

   “He had no speech prepared, so he improvised.”

   “They improvised a simple shelter with branches and the rope they were carrying.”

   “She improvised a lovely solo.”

   “We have improvised the most charming party imaginable. The summer has come back by surprise. I own I wonder that June was not tired of us: still here is a day so sunny, that October does not know its own. The Duke of Wharton, Lord Hervey, and some two or three others, have designed a water-party in our honour.”

   “As this terrible emotion took charge of him, he found himself improvising a whole series of lovers for her, imagining them to be waiting around every corner.”