Definition of immitigable in US English:

immitigable

adjective

archaic
  • Unable to be made less severe or serious.

    ‘the pain was immitigable’

Origin

Late 16th century: from late Latin immitigabilis, from in- ‘not’ + mitigabilis ‘able to be mitigated’.

Pronunciation

immitigable

/ɪ(m)ˈmɪdəɡəb(ə)l//i(m)ˈmidəɡəb(ə)l/