Longman Dictionary of Contemporary English
Wiktionary
n. (context idiomatic English) A person of conventional morality
WordNet
n. a frank and honest person [syn: square shooter, straight shooter] [ant: liar]
Wikipedia
The Straight Arrow radio program was a western adventure series for juveniles which was broadcast, mostly twice weekly in the United States from 1948 or 1949 through 1951. A total of 292 episodes were aired.
Although first broadcast only in California, in early 1949 it was broadcast nationally on the Mutual Broadcasting Network. All the programs were written by Sheldon Stark.
The protagonist, rancher Steve Adams, became the Comanche Indian, the Straight Arrow, when bad people or other dangers threatened. In fact, Adams was a Comanche orphan who had been adopted by the Adams ranching family and later inherited the ranch. His dual identity was known to only one friend. Internal evidence places the ranch in the vicinity of the Colorado Rockies in the 1870s. Howard Culver played both Adams and Straight Arrow.
The program was sponsored by Nabisco Shredded Wheat cereal.
Usage examples of "straight arrow".
Among my people, we call a person who behaves with honor a 'straight arrow.