| haphazard(adjective, erratic, random) |
| contingent(adjective, uncertainty, chance, secondary, subsidiary) |
| exceptional(adjective, special, irregular, sporadic) |
| sparse(adjective, light, slight, thin, strange) |
| uncertain(adjective, chance, irregular, unreliable, uneven) |
| unsystematic(adjective, erratic, random, haphazard) |
| accidental(adjective, chance, secondary, subsidiary, related) |
| adventitious(adjective, chance, secondary, subsidiary, related) |
| discontinuous(adjective, irregular, unreliable, uneven, variable) |
| especial(adjective, special, irregular, sporadic) |
| exclusive(adjective, special, irregular, sporadic) |
| periodical(noun, adjective, continue) |
| special(adjective, irregular, sporadic) |
| uneven(adjective, unreliable, variable) |
| broken(adjective, irregular, erratic, infrequent, recurrent) |
| chance(noun, adjective, irregular, secondary, subsidiary) |
| circumstantial(adjective, circumstantial) |
| extra |
| provisional(adjective, uncertainty) |
| variable(adjective, unreliable, uneven) |