Sinister and Unmitigable

Sinister adjective - Being or showing a sign of evil or calamity to come.

Unmitigable and sinister are semantically related In some cases you can use "Unmitigable" instead an adjective "Sinister".

Unmitigable adjective - Incapable of being mitigated.

Sinister and unmitigable are semantically related in hopeless topic. Sometimes you can use "Sinister" instead an adjective "Unmitigable", if it concerns topics such as futile.