1. A sharp, pointed structure or appendage, especially a sting or prickle in plants and animals.
Usage: technical; biology; plural: aculei
2. In entomology, a needle-like ovipositor or sting found in certain insects.
Usage: zoology; technical

Examples

• The bee's aculeus is a modified ovipositor used for defense.
• Many plants have small aculei on their stems to protect against herbivores.
• The wasp's aculeus allows it to inject venom into its prey.
• Botanists examined the aculei covering the cactus surface.
• The aculeus of the scorpion contains a potent toxin.