boot 2 
(bt)
(bt)intr.v. boot·ed, boot·ing, boots
To be of help or advantage; avail.
n.
Idiom: 1. Chiefly Southern & Midland US See lagniappe.
2. Archaic Advantage; avail.
to boot
In addition; besides: The new cruise ship was not only the biggest in the world, but the fastest to boot.
[Middle English boten, to be of help, from Old English bōtian, from bōt, help; see bhad- in the Appendix of Indo-European roots.]