boot 2 
(b
t)
intr.v. boot·ed,
boot·ing,
boots To be of help or advantage; avail.
n.1. Chiefly Southern & Midland US See lagniappe.
2. Archaic Advantage; avail.
Idiom: 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.]