| spontaneous(adjective, plain, natural, thoughtless, impulsive) |
| impulsive(adjective, simple, natural, casual, thoughtless) |
| involuntary(adjective, simple, natural, casual, thoughtless) |
| unpremeditated(adjective, passionate, violent, impulse, abrupt) |
| natural(adjective, simple, casual, impulsive, willing) |
| unmeditated(adjective, passionate, violent, impulse, abrupt) |
| unthinking(adjective, natural, instinctive, unwilling, automatic) |
| voluntary(adjective, simple, natural, casual, impulsive) |
| accustomed(adjective, natural, instinctive, automatic, inherent) |
| congenital(adjective, natural, instinctive, automatic, inherent) |
| extemporaneous(adjective, simple, plain, violent, natural) |
| habitual(adjective, natural, instinctive, unwilling, automatic) |
| impromptu(adjective, adverb, simple, plain, natural) |
| inborn(adjective, natural, instinctive, automatic, inherent) |
| ingrained(adjective, natural, instinctive, automatic, inherent) |
| inherent(adjective, natural, instinctive, automatic, innate) |
| innate(adjective, natural, instinctive, automatic, inherent) |
| instinctive(adjective, simple, passionate, violent, natural) |
| intrinsic(adjective, natural, instinctive, automatic, inherent) |
| intuitional(adjective, natural, instinctive, automatic, inherent) |