Achene

any small, dry, hard, one-seeded, indehiscent fruit.
Historical Examples

achene obtusely triangular, partly 3-celled, enclosed in the indurated calyx.
The Manual of the Botany of the Northern United States Asa Gray

Name from , a bug, and , resemblance; from the form of the achene.
The Manual of the Botany of the Northern United States Asa Gray

Ovary 1-celled with a suspended ovule, becoming an achene; calyx none; aquatic herbs, with finely dissected whorled leaves.
The Manual of the Botany of the Northern United States Asa Gray

Fruit usually an achene, compressed or 3–4-angled or -winged.
The Manual of the Botany of the Northern United States Asa Gray

achene triangular, pointed with the persistent base of the style.
The Manual of the Botany of the Northern United States Asa Gray

Calyx 6-parted or -cleft, colored, persistent about the achene.
The Manual of the Botany of the Northern United States Asa Gray

The modified calyx-limb in Composit, forming a crown of very various character at the summit of the achene.
The Manual of the Botany of the Northern United States Asa Gray

The pappus consists of a tuft of simple hairs, most of which are longer than the achene.
Field and Woodland Plants William S. Furneaux

achene elliptical, closely invested by the dry and persistent compressed calyx.
The Manual of the Botany of the Northern United States Asa Gray

The nut or achene—a fruit with hard and dry walls, as the filbert and the acorn.
Field and Woodland Plants William S. Furneaux

noun
a dry one-seeded indehiscent fruit with the seed distinct from the fruit wall. It may be smooth, as in the buttercup, or feathery, as in clematis
achene also akene
(ā-kēn’)
A small, dry, one-seeded fruit in which the seed sits free inside the hollow fruit, attached only by the stem of the ovule. Achenes are indehiscent (they do not split open when ripe). The fruits of the sunflower and elm are achenes.