| impromptu(adjective, adverb, simple, informal, natural) |
| extemporaneous(adjective, adverb, simple, informal, natural) |
| extempore(adjective, simple, informal, natural, straightforward) |
| offhand(adjective, adverb, simple, natural, chance) |
| ad-lib(verb, adjective, adverb, produce, simple) |
| extemporary(adjective, prepared, spontaneous, unprepared, impromptu) |
| improvised(adjective, adverb, simple, informal, natural) |
| unrehearsed(adjective, impulsive, prepared, impromptu, unplanned) |
| spur-of-the-moment(adjective, impulsive, prepared, spontaneous, unprepared) |
| offhanded |
| snap(adjective, prepared, spontaneous, unprepared, impromptu) |
| spontaneous(adjective, simple, informal, natural, straightforward) |
| makeshift(adjective, informal, spontaneous, offhand, unprepared) |
| unplanned(adjective, simple, informal, natural, chance) |
| unprepared(adjective, informal, spontaneous, impromptu, unplanned) |
| ad hoc(expression, adjective, informal, spontaneous, unprepared) |
| ad lib(expression, adjective, produce, bear, impulsive) |
| automatic(adjective, simple, natural, casual, impulsive) |
| casual(adjective, simple, easy, plain, natural) |
| expedient(adjective, spontaneous, unprepared, impromptu, unrehearsed) |