extemporary

Spoken, done, or composed with little or no preparation or forethought. See synonyms at extemporaneous.

[From EXTEMPORE.]

adjective

Spoken, performed, or composed with little or no preparation or forethought: ad-lib, extemporaneous, extempore, impromptu, improvised, offhand, snap, spur-of-the-moment, unrehearsed. Informal off-the-cuff. See prepared/unprepared.

The adjective has one meaning:

Meaning #1: with little or no preparation or forethought
  Synonyms: ad-lib, extemporaneous, extempore, offhand, offhanded, off-the-cuff, unrehearsed