| toss-up |
| treacherous(delicate, uncertain, insecure, rugged, risky) |
| tricky(adjective, delicate, uncertain, unstable, doubtful) |
| trustless(uncertain, doubtful, unsure) |
| unassured(adjective, uncertain, nervous, doubtful, hesitant) |
| uncertain(adjective, delicate, nervous, unstable, doubtful) |
| unclear(adjective, uncertain, nervous, doubtful, vague) |
| unconfident(adjective, uncertain, anxious, nervous, doubtful) |
| unconfirmed(doubtful, vague, unsure, risky) |
| unconvinced(adjective, uncertain, nervous, doubtful, hesitant) |
| undecided(uncertain, nervous, doubtful, vague, dubious) |
| undecided issue |
| undependable(adjective, uncertain, nervous, doubtful, dubious) |
| undetermined(doubtful, vague, dubious, unsure, arguable) |
| unfixed(doubtful, vague, unsure) |
| unforeseeable(doubtful, vague, changeable, unsure, erratic) |
| unhealthy(adjective, delicate, uncertain, unstable, doubtful) |
| unlikely(uncertain, doubtful, unsure) |
| unpredictable(adjective, uncertain, doubtful, vague, changeable) |
| unreliable(adjective, delicate, uncertain, nervous, unstable) |