Here are examples of the word/phrase "doubtfulness" used in a sentence and paraphrased in a sentence...
There was too much doubtfulness among eachother to have a relationship built on trust.
There was too much dubiousness among eachother to have a relationship built on trust.
The judge was given too much reason to harbor doubtfulness towards the defendant.
The judge was given too much reason to harbor dubiousness towards the defendant.
Other Examples...