| doubting(verb, adjective, weak, uncertain, shy) |
| falter |
| flexible(adjective, changeable, fickle, variable, volatile) |
| flimsy(adjective, weak, delicate, ill, sick) |
| fluid(adjective, unstable, unsettled, unpredictable, unreliable) |
| flutter |
| fly-by-night(adjective, uncertain, nervous, doubtful, dubious) |
| frail(adjective, weak, delicate, unstable, ill) |
| lingering(verb, adjective, procrastinating) |
| movable(adjective, unstable, unsettled, changeable, uneven) |
| protean(adjective, unstable, unsettled, unpredictable, unreliable) |
| puzzling |
| questionable(adjective, doubtful, vague, hesitant, unpredictable) |
| rocking(verb, oscillating) |
| rocky(adjective, weak, unstable, unsettled, shaky) |
| scatterbrained(adjective, capricious) |
| shilly-shally(adjective, irresolute) |
| shrinking(adjective, nervous, shy, fearful, irresolute) |
| shy(adjective, uncertain, nervous, doubtful, hesitant) |
| sickly(ill, sick, unwell) |