Adjective
absurd - (of an idea or suggestion) wildly unreasonable, illogical, or inappropriate

When Edwin Hubble in 1929 suggested that some of the little dots of light in the sky were other galaxies, many people though the idea was absurd, but he was proven to be correct.
reticent - Describing someone who is inclined to keep their thoughts, feelings, or personal matters to themselves, not expressing them freely.

He was reticent about discussing his past, thinking that there were details that she might not react well too.