Unexceptionable and unexceptional look similar, but they make different judgments. One concerns whether something is acceptable; the other concerns whether it stands out.
Unexceptionable means acceptable and not reasonably open to criticism or objection. Choose it when you want to say that someone’s conduct, a statement, or a proposal gives you no good reason to complain.
- Her behavior during the interview was unexceptionable.
- The report offered an unexceptionable account of the facts.
This is a formal word. In everyday conversation, perfectly acceptable or nothing to object to may sound more natural. It does not necessarily mean brilliant or impressive: something can be entirely acceptable without being exciting.
Unexceptional means ordinary or not especially impressive. Choose it when something is much like others of its kind and has no remarkable qualities.
- The hotel was clean but unexceptional.
- His exam results were unexceptional, though good enough to pass.
This word is not necessarily a harsh criticism. It can simply indicate that something is average. In a review, however, it may suggest mild disappointment because the experience did not stand out.
Consider two descriptions of a speech: unexceptionable suggests that its content was acceptable and gave no reasonable grounds for objection. Unexceptional suggests that the speech was ordinary or forgettable. A speech could be both: there might be nothing wrong with it, but nothing memorable about it either.