to boot

boot 2   (bōōt)    intr.v.   boot·ed, boot·ing, boots To be of help or advantage; avail. n.   Chiefly Southern & Midland U.S. See lagniappe. Archaic Advantage; avail. [Middle English boten, to be of help, from Old English bōtian, from bōt, help; see bhad- in Indo-European roots.]

Main Entry: boot
Function: noun
Etymology: obsolete or dialect boot compensation, from Old English bOt advantage, compensation
: additional money or property received to make up the difference in an exchange of business or investment property that is of like kind but unequal in value
NOTE: Under Internal Revenue Code section 1031, no tax liability results from an exchange solely of like-kind property used in a business or trade or held for investment. If the exchange includes boot, however, under section 1245 the boot will be treated as ordinary income.

to boot

Besides, in addition. For example, It rained every day and it was cold to boot, or He said they'd lower the price of the car by $1,000 and throw in air conditioning to boot. This expression has nothing to do with footwear. Boot here is an archaic noun meaning "advantage," and in the idiom has been broadened to include anything additional, good or bad. [c. a.d. 1000]