I assume you're referring to an aircraft.
Straight and level flight is achieved in an aeroplane, glider or airborne vehicle when lift is approximately equal to drag - eg. The craft is not rising or descending, providing the 'level flight'. In addition, the roll of the aircraft is usually neutral, providing the 'straight', and thrust is approx. equal to drag to maintain a constant speed.
straight, as in rectilinear which is a straight line.
A straight angle is by definition 180°.
Yes. Line segments are straight, by definition.
my ass!
No. By definition, straight women are only attracted to men.
The shortest distance between two points is... a straight line.
Two straight lines that meet.
It is a ruler with 12 inches on it
a graph that does not have a straight line
Motion in a straight line.
Doubt there is a specific definition for a straight penis. Terminology-wise, a penis is a penis. But in my opinion "schlong" sounds like it should be given that meaning :3
If you are looking for a straight definition, I suggest you use www.dictionary.com and look it up there.