noun
square person; trustworthy person
Describes a person who is honest, reliable, and morally upright; often used in contrast to someone who is cunning or untrustworthy.
彼はかたじんだから、約束は必ず守る。
He's a square person, so he always keeps his promises.
あの人はかたじんで、嘘をつくような人ではない。
That person is trustworthy and not the type to tell lies.