英语词源字典 - 在线词源网站

extempore (adv.)[extempore 词源字典]: 1550s, from Latin phrase ex tempore "offhand, in accordance with (the needs of) the moment," literally "out of time," from ex "out of" (see ex-) + tempore, ablative of tempus (genitive temporis) "time" (see temporal). Of speaking, strictly "without preparation, without time to prepare," but now often with a sense merely of "without notes or a teleprompter." As an adjective and noun from 1630s.[extempore etymology, extempore origin, 英语词源]
off-hand (adv.): also offhand, 1690s, "at once, straightway," from off (adv.) + hand (n.). Probably originally in reference to shooting without a rest or support. Hence, of speech or action, "unpremeditated" (1719). Related: Off-handed; off-handedly.
slapdash (adv.): 1670s, from slap (v.) + dash (v.). As an adjective, "dashing, offhand, careless," from 1792. As a noun, "rough-coat, coarse plaster," from 1796.