If I had I'd have said the same as you - the name of a straight line between two points on the circumference of a circle is "chord", and the length of the longest such line you can construct is the diameter of the circle.
And so you'd be wrong, as JohnW2 outlined earlier
Thanks for that Ban.
I'm glad you held off defying, I wanted to give others the chance to answer first 'cos I knew Diameter would be a popular answer and didn't want you to thunder in with the proper answer too early.
Not that he's provided the 'proper answer', as JohnW2 outlined earlier
OED Online said:diameter, n.
1.
a. Geom. A straight line passing through the centre of a circle (or sphere), and terminated at each end by its circumference (or surface). Hence extended to a chord of any conic (or of a quadric surface) passing through the centre; and further, to a line passing through the middle points of a system of parallel chords (or through the centres of mean distances of their points of intersection with the curve), in a curve of any order.