What does "jacob" mean?

Jacob: Jacob's ladder. (a) (Bot.) A perennial herb of the genus Polemonium (P. coeruleum), having corymbs of drooping flowers, usually blue. Gray. (b) (Naut.) A rope ladder, with wooden steps, for going aloft. R. H. Dana, Jr. (c) (Naut.) A succession of short cracks in a defective spar. -- Jacob's membrane. See Retina. -- Jacob's staff. (a) A name given to many forms of staff or weapon, especially in the Middle Ages; a pilgrim's staff. [Obs.] Spenser. (b) (Surveying) See under Staff.