Definition of unpremeditable in US English:

unpremeditable

adjective

  • That cannot be premeditated; impossible to anticipate or foresee.

Origin

Mid 18th century; earliest use found in Laurence Sterne (1713–1768), writer and Church of England clergyman. From un- + premedit- + -able.

Pronunciation

unpremeditable

/ˌʌnprɪˈmɛdɪtəbl/