Easton's Bible Dictionary (1897)
Occurs only once, in the account of Jacob’s vision (Gen. 28:12).
Hastings' Dictionary of the Bible (1898) & Schaff's Bible Dictionary
LAD'DER (Heb. a staircase, from the verb "to raise up"), the object seen by Jacob in his vision. Gen 28:12. The use of the word in other writers suggests that the patriarch saw mountains or rocks piled up as a staircase. It was a symbol of communion with heaven through Christ. See John 1:51.