From in- + probability.

• (RP) IPA: /ɪmˌpɹɒb.əˈbɪl.ɪ.ti/
• (America) IPA: /ɪmˌpɹɑb.əˈbɪl.ə.ti/, [ɪmˌpɹɑb.əˈbɪl.ə.ɾi], /ɪmˌpɹɑb.əˈbɪl.ɪ.ti/, [ɪmˌpɹɑb.əˈbɪl.ɪ.ɾi]

improbability

1. The quality or state of being improbable; unlikelihood.
2. That which is improbable; an improbable event or result.
   • 1838 (date written), L[etitia] E[lizabeth] L[andon], chapter X, in Lady Anne Granard; or, Keeping up Appearances. […], volume I, London: Henry Colburn, […], published 1842, →OCLC ↗, page 130 ↗:

     "I really," returned the other with a sneer, "cannot agree about probabilities or improbabilities, but I know what the generality will think when they see a gentleman constantly with five very pretty girls, and I also know what they will say."

• Spanish: improbabilidad