I may be outdated, but when I was in school we called that a line segment. I am assuming u mean a straight line. If it is a circle or other curved line, it is called an arc.
In the case of upper case letters in the Roman alphabet, and allowing tine segments of lines that are curved, they are: B, C, D, E, F, G, H, M, N, O, P, Q, R, S, U, Z.
you can make you,no,cab,cat,train,rack
A, b, c, d, g, j, k, l, o, p, q, r, s, t, u, v, x, y
Capital letters or big letters. ex. A G L U E The opposite of lowercase letters. (a g l u e )
no j is a consonant a e i o u are vowels
C,o,s,u
Jaguar Ulysses Butterfly
List: O Q Z J..............etc
haji
B, J, O, U, and Y
u g y h j
cajole
jurants
B, J, O,U, And Y
You can spell many, many, many words with those letters.
Well, darling, the letters of the alphabet that have no straight lines are O, C, S, U, V, W, Y, and Z. So, if you're looking for some curvy, sassy letters, those are the ones you're after. Hope that clears things up for you!