achenium

from The Century Dictionary.

• noun In botany, a small, dry and hard, one-celled, one-seeded, indehiscent fruit; strictly, a single and free carpel of this character, as in the buttercup, avens, etc., but extended to all similar fruits resulting from a compound ovary, even when invested with an adnate calyx, as in the order Compositæ. Also written achene, achænium, akene, and akenium.
• noun In entomology, a genus of beetles.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun botany achene