The quality of being small-minded — the noun for it. It names the attitude itself, rather than describing a person.

So you use it when you want to talk about the fault as a thing: something that exists in a place, in a group, in an era, and that can be met, fought, or grown out of. "The small-mindedness of the village drove her to the city." "There is a lot of small-mindedness in these arguments." Because it turns the criticism into an abstract thing, it can feel slightly less personal than calling someone small-minded to their face — you are attacking the attitude in the room, not naming the man who holds it. Politicians and writers use that trick often.

It carries both halves of the adjective: petty fussing over trifles, and a hard refusal to accept anything unfamiliar. Which one is meant usually comes clear from what surrounds it.

It is a long, slightly formal-sounding word, and it lives more in writing and speeches than in everyday chat. In conversation people simply say "he's so small-minded".