doubtful ▼ (improbable or unlikely) adjective [UK: ˈdaʊt.fʊl] [US: ˈdaʊt.fəl]
far-fetched ▼ (not likely) adjective [UK: ˈfɑː(r) fetʃt] [US: ˈfɑːr ˈfetʃt]
implausible ▼ (unlikely) adjective [UK: ɪm.ˈplɔː.zɪb.l̩] [US: ˌɪm.ˈplɒ.zəb.l̩]
impossible ▼ (never happening) adjective [UK: ɪm.ˈpɒ.səb.l̩] [US: ˌɪm.ˈpɑː.səb.l̩]
improbable ▼ (not likely to happen) adjective [UK: ɪm.ˈprɒ.bəb.l̩] [US: ˌɪm.ˈprɑː.bəb.l̩]
incredible ▼ (too implausible to be credible) adjective [UK: ɪn.ˈkre.dəb.l̩] [US: ˌɪn.ˈkre.dəb.l̩]
incredulous ▼ (difficult to believe; incredible) adjective [UK: ɪn.ˈkre.djʊ.ləs] [US: ˌɪn.ˈkre.dʒə.ləs]
tall [taller, tallest]▼ (of a story) adjective [UK: tɔːl] [US: ˈtɒl]
unbelievable ▼ (incredible) adjective [UK: ˌʌn.bɪ.ˈliː.vəb.l̩] [US: ˌʌn.bə.ˈliː.vəb.l̩]
unlikely [unlikelier, unlikeliest]▼ (not likely) adjective [UK: ʌn.ˈlaɪ.kli] [US: ʌn.ˈlaɪ.kli]
unthinkable ▼ (inconceivable or unimaginable; extremely improbable in a way that goes against common sense) adjective [UK: ʌn.ˈθɪŋk.əb.l̩] [US: ʌn.ˈθɪŋk.əb.l̩]