extemporaneous

American Heritage® Dictionary of the English Language, Fourth Edition

1. adj. Carried out or performed with little or no preparation; impromptu: an extemporaneous piano recital.
2. adj. Prepared in advance but delivered without notes or text: an extemporaneous speech.
3. adj. Skilled at or given to unrehearsed speech or performance: an accomplished extemporaneous speaker.
4. adj. Provided, made, or adapted as an expedient; makeshift: an extemporaneous policy decision.

Century Dictionary and Cyclopedia

1. Made, done, furnished, or procured at the time, without special preparation; resulting from or provided for the immediate occasion; unpremeditated: as, an extemporaneous address or performance; extemporaneous support or shelter.
2. Synonyms Extemporaneous, Unpremeditated. There is now some disposition to apply extempore and extemporaneous to that which is unpremeditated only in form. Extemporaneous speaking or preaching is, by this view, carefully prepared in thought, arrangement, etc., only the choice of words and phraseology being left to the inspiration of the moment. Extemporary has not this sense. Unpremeditated is thus opposed to premeditated, and extemporaneous to written or recited.
3. In pharmacy, noting a preparation which is compounded at the time it is ordered, in distinction from a ready-made, or officinal preparation.

Wiktionary

1. adj. without preparation or advanced thought; offhand

GNU Webster's 1913

1. adj. Composed, performed, or uttered on the spur of the moment, or without previous study; unpremeditated; off-hand; ad-lib; extempore; extemporary.

WordNet 3.0

1. adj. with little or no preparation or forethought