Jamieson, Fausset & Brown, on Judg 14:18

“And they on the seventh day before the sun went down said to him: What is sweeter than honey? and what is stronger than a lion? And he said to them: If you had not ploughed with my heifer, you had not found out my riddle.”

“If ye had not plowed with my heifer, ye had not found out my riddle--a metaphor borrowed from agricultural pursuits, in which not only oxen but cows and heifers were, and continue to be, employed in dragging the plough. Divested of metaphor, the meaning is taken by some in a criminal sense, but probably means no more than that they had resorted to the aid of his wife--an unworthy expedient, which might have been deemed by a man of less noble spirit and generosity as releasing him from the obligation to fulfil his bargain.”

Imported from an open dataset — not yet checked against the printed edition.