1. Concave on one side and convex on the other with the concavity being greater than the convexity

See also: concave

• black sage
• black sally
• black salsify
• black saltwort
• Black Sea
• black sea bass
• Black September
• Black September Movement
• black sheep
• black snakeroot
• black spleenwort
• black spot
• black spruce
• black squirrel
• black stork
• black stump
• black sumac
• black swan
• Black Tai
• black tea
• black tongue
• black tree fern
• black turnstone
• Black Vernacular
• Black Vernacular English