Unexceptionable is an adjective that describes something or someone as not likely to cause someone’s disapproval or disdain.
It is the opposite of exceptionable or something that is likely to cause disapproval or objection.
The noun form is unexceptionableness and the adverb form is unexceptionably.
Unexceptional is an adjective used to describe something as ordinary or without qualities that make it stand out from others of its kind.
It is the opposite of exceptional or something that is very out of the ordinary and the best of its field.
The adverb form for this word is unexceptionally.
The usage of the positive forms of these words is clear, but sometimes unexceptionable can be a synonym for unexceptional. The reason being that something can not cause one to object simply because it is too ordinary to cause any kind of comment or opinion at all, whether good or bad.
Examples
Compared to these underlying structural changes the campaign’s conventional focus on differences in economic, health, housing and social policy has been unexceptionable, reflecting well-established party positions. [The Irish Times]
This perception is, above all, what remains after viewing “Red Hollywood”: for better or worse, wide-ranging political critique has been integrated, unexceptionably and unproblematically, into the new mainstream. [The New Yorker]
A modest debut and an equally unexceptional farewell marked Shukla’s cricket career, which was interspersed with some robust all-round show that gave him a distinct identity among the top spinners of the country. [The Hindu]
Hutcherson and Hemsworth continue to be unexceptionally fine. [Variety]