ad lib
ad-libBrE /ˌæd ˈlɪb/
NAmE /ˌæd ˈlɪb/
verb
verb forms(-bb-) [intransitive, transitive]to say sth in a speech or a performance that you have not prepared or practised 
word origin
improvise
She abandoned her script and began ad-libbing.~ sth I lost my notes and had to ad-lib the whole speech.He ad-libbed his way through the meeting. 
ad lib /BrE ˌæd ˈlɪb; NAmE ˌæd ˈlɪb/ nounThe speech was full of ad libs. ad lib /BrE ˌæd ˈlɪb; NAmE ˌæd ˈlɪb/ adjectivean ad lib speech ad lib /BrE ˌæd ˈlɪb; NAmE ˌæd ˈlɪb/ adverbShe delivered her lines ad lib.
