1. Plural of blueback; small fish with blue or blue-green coloring on the back, especially young herring or similar species.
Usage: chiefly nautical or commercial fishing; often used in plural form
2. Historical: Confederate paper money or currency from the American Civil War era, named for the blue ink used on the reverse side.
Usage: historical; chiefly U.S.

Examples

• The fishermen hauled in nets full of bluebacks during the spring run.
• Bluebacks are a common bait fish used by commercial and recreational anglers.
• Collectors of Civil War memorabilia often seek rare bluebacks from the 1860s.
• The school of bluebacks darted through the shallow waters near the shore.
• During the war, soldiers were sometimes paid in bluebacks instead of gold.