noun

• (botany) A sharp, tapering point extending from a plant.
  "The black star of the corolla, characteristic of the original form, the manyfloweredness of the inflorescence (often connected with [3]—4 whirls), upper leaves in the inflorescence, adpression of the acumina of the calyx, its size, the closely situated anthers, long pistils, the length of the pedicel above and below the articulation and the thickness of the pedicel dominate."
• (anatomy) A bony, often sharp, protuberance, especially that of the ischium.
  "The rostrum is the anterior extension of the carapace between the eyes. It ends in a more or less acute tip, or acumen, and may have a lateral spine on each side or bear a longitudinal keel (carina) on the dorsal surface."