Relating to something that is only slightly connected to the main thing.
Tangential things are not very important to the main thing.
Examples:
The teacher's story was tangential to the lesson.
She asked a tangential question that didn't really fit.
The tangential idea was interesting, but not helpful.
The tangential comment made everyone laugh.
His explanation was so tangential, it took an hour!
The tangential path led us to a surprise.