extemporize

/EH1 K S T EH0 M P ER0 AY0 Z/
verb
  1. 1

    To do something, particularly to perform or speak, without prior planning or thought; to act in an impromptu manner; to improvise.

  2. 2

    To do, create, improvise, adapt, or devise in an impromptu or spontaneous manner.

Source: https://en.wiktionary.org/wiki/extemporize