(colloquial) Not using alcohol, drugs, etc. [from 20th c.]
(mathematics) concerning the property allowing the parallel-transport of vectors along a course that keeps tangent vectors remain tangent vectors throughout that course (a course which is straight, a straight curve, is a geodesic)
“It was her mother who broke the deadlock and marched her over to a beauty school to have the stylists turn her straightish hair into an Afro.”
“I think he genuinely doesn't understand why a nice straightish boy like me wants to go to gay clubs anyway.”
“It was her mother who broke the deadlock and marched her over to the Beauty School to have the renowned stylists turn her straightish hair into an Afro.”