What does the Wife of Bath mean by "engender"?

The Wife of Bath uses this word in line 465, when she says,

For al so siker as cold engendreth haylA likerous mouth moste han a likerous tayl.

In modern English, this means something like: "For just as surely as cold engenders hail, a gluttonous or greedy mouth must have a lecherous tail." She is using the word in the same sense that it would be used in modern English—effectively, to engender something means to bring forth or give birth to it. So, here, she is saying that cold engenders hail in the sense that cold gives rise to hail, or leads to this kind of weather; hail does not exist when it isn't cold, and when it is cold, there is a high likelihood that this cold will produce hail or snow. She is using this as an example of something which is "siker," or sure; there is a direct causality between the two things. Something which is as likely as cold giving rise to hail is something that is very likely indeed.