Root: tang (meaning "to touch, to seize, to grasp")
Words:
* Tangent: A line that touches a curve at one point but does not intersect it.
* Tangential: Relating to or resembling a tangent; not central or essential.
* Intangible: Unable to be touched or grasped; not material.
* Contingent: Dependent on something else; possible but not certain.
* Tangent: A sudden change of course or subject.
* Tangible: Something that can be touched or grasped; real and concrete.
* Tangen: (archaic) To touch or grasp.
Let me know if you'd like more examples!