Definition of extemporize in US English:

extemporize

verb

[no object]
  • Compose, perform, or produce something such as music or a speech without preparation; improvise.

    ‘he extemporized at the piano’
    with object ‘she was extemporizing touching melodies’
    improvise, ad lib, play it by ear, think on one's feet, cobble something together, throw something together, make it up as one goes along, take it as it comes
    View synonyms

Pronunciation

extemporize

/ɪkˈstɛmpəˌraɪz//ikˈstempəˌrīz/