extemporize

extemporize
extemporise, / ɪkˈstempəraɪz; ɪk`stɛmpəˌraɪz/ v [I]
(fml 文) speak or perform extempore 即席讲话; 即兴表演
    He had to extemporize because he had forgotten to bring his notes. 他因为忘了带讲稿, 只好即席发言.

牛津英汉双解词典