ad lib vs do something on the spur of the moment

ad lib

adv

Extemporaneously.
At will.
To whatever extent.
At pleasure.

verb

To perform without preparation.
To perform without script.
To perform extemporaneously.

adj

Extemporaneous, impromptu.

do something on the spur of the moment

How often have the words ad lib and do something on the spur of the moment occurred in a corpus of books? (source: Google Ngram Viewer )