Definition of "forwhy"

Then did he cast to steale her thence away, / And with him beare where none of her might know: / But all in vaine, for-why he found no way / To enter in […]

1596, Edmund Spenser, The Faerie Queene, IV.12

But of the day—and of the weeks bygone, and of many other things—this deponent saith nil, whereby and forwhy he is going to bed.

1863 February 22, Edward Lear, Letter from Edward Lear to Fortescue