1. a small leaflet or subdivision of a compound leaf, especially in ferns
Usage: botanical
2. a small fin-like appendage or projection on certain marine animals
Usage: zoological

Examples

• Each pinnule on the fern frond was delicately shaped and green.
• The botanist examined the pinnules under a magnifying glass.
• The compound leaf consisted of numerous small pinnules arranged along the stem.
• Marine biologists studied the pinnules of the sea lily specimens.
• The fern’s pinnules turned brown as autumn approached.
• Each pinnule served as a tiny photosynthetic unit for the plant.