What is the meaning of straight?
STRAIGHT: adj. 1. without a bend, angle, or curve; not curved. A straight road ○ straight hair. 2. In a position that is exactly vertical or horizontal. That shelf’s not straight. 3. In a series one after another. They’ve won five straight games so far. 4. Honest. A straight answer ○ I don’t think he was being straight with me. 5. An alcoholic drink that is straight is not mixed with water, ice, etc.
(take from Cambridge Learner’s Dictionary, second edition, 2004)

Etymology: mid-14c., “direct, undeviating, not crooked”. Meaning "true, direct, honest" is from 1520s



What is the meaning of curved?
CURVED: adj. 1. Not straight. 2. Having or marked by a curve or smoothly rounded bend. The curved tusks of a walrus ○ His curved lips suggested a smile but his eyes were hard
(take from WordReference English Dictionary in http://wordreference.com/definition/ curved)

Etymology: early 15c. "crooked, curved, bent". The noun is attested from 1690s, "curved line"; with ref. to the female figure (usually pl.) from 1862.