Jacob's ladder

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. Nautical A rope or chain ladder with rigid rungs.
2. n. Any of various plants of the genus Polemonium, especially P. caeruleum, having blue flowers and alternate, pinnately compound leaves with numerous leaflets.

Century Dictionary and Cyclopedia

1. n. Nautical, a rope ladder with wooden steps or spokes by which to go aloft. Also called jack-ladder.
2. n. A common garden-plant of the genus Polemonium, the P. cæruleum, belonging to the natural order Polemoniaceæ: so called from the ladder-like arrangement of its leaves and leaflets. It is a favorite cottage-garden plant, and is found in temperate and northern latitudes in most parts of the world. It grows tall and erect, about 1½ feet high, with alternate pinnate, smooth, bright-green leaves, and terminal corymbs of hand some blue (sometimes white) flowers. The name is sometimes locally applied to several other plants.
3. n. A toy in which pieces of cardboard, wood, glass, or other material are so connected, one above another, with strings or tapes, that when the highest one is inverted those below it invert themselves in succession.
4. n. The carrion-flower, Smilax herbacea.

Wiktionary

1. n. A flowering plant of the genus Polemonium.
2. n. nautical A vertical ladder from the ratline to the upper masts.
3. n. A toy consisting of blocks of wood, held together by strings or ribbons, that appear to cascade downward as they flip over.
4. n. A pocketknife consisting of two handle segments joined by a pivot, with a blade connected by a second pivot to the end of one handle segment.
5. n. mathematics A noncompact surface resembling a ladder made of handlebodies.

GNU Webster's 1913

1. n. (Bot.), (Naut.), (Naut.) A succession of short cracks in a defective spar.

WordNet 3.0

1. n. (nautical) a hanging ladder of ropes or chains supporting wooden or metal rungs or steps
2. n. pinnate-leaved European perennial having bright blue or white flowers