Tangential means only slightly connected to the main point. A tangential remark.
The picture is a tangent, a line that touches a curve at one point and goes off. A tangential question is not always useless, since it is where a good deal of discovery comes from.
1adjectivetangentialOnly slightly connected to the main point.
“The whole discussion went tangential about ten minutes in.”
tangential is a quality.
From tangent + -ial.
Etymology from Wiktionary, CC BY-SA