offhand

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adverb Without preparation or forethought; extemporaneously.
• adjective Performed or expressed without preparation or forethought.

from The Century Dictionary.

• At once; without deliberation or premeditation; without previous preparation or practice.
• From the hand; without the support of a rest.
• Without study or premeditation; impromptu: as, an offhand remark; an offhand speech.
• Free and easy; unstudied or unconventional: as, an offhand manner.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Instant; unprepared; ready; extemporaneous; unrehearsed

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective without planning or thinking ahead
• adjective careless; without sufficient thought or consideration
• adjective curt, abrupt, unfriendly
• adverb right away, immediately, without thinking about it
• adverb in an offhand manner

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adverb without preparation
• adverb in a casually inconsiderate manner
• adjective with little or no preparation or forethought
• adjective casually thoughtless or inconsiderate
• adverb without previous thought or preparation