What does "unthinkable" mean?

Something, or various things collectively, that one dare not think about, dare not do, or dare not think about doing.

What is a synonym for "unthinkable"?

Common synonyms include: inconceivable, a bit thick, a bit thin, absurd, barred, beyond belief.

Pronounced //ʌnˈθɪŋkəbəl//.

//ʌnˈθɪŋkəbəl// adj, noun

adj, noun ·Moderate ·College level

Noun

1
Something, or various things collectively, that one dare not think about, dare not do, or dare not think about doing.
"Near-synonym: unspeakable"

Adjective

1
That cannot be believed.
"Near-synonyms: unbelievable, incredible, inconceivable"
2
Inconceivable or unimaginable; extremely improbable in a way that goes against common sense.
"Near-synonyms: inconceivable, imponderable"
3
Extremely improper; extremely at odds with norms of expected behavior.
"Near-synonyms: taboo, unspeakable, unutterable, inconceivable"