A word puzzle which arose from the definition of arothelp: find words which when reversed (approximate reversal is acceptable) yield another word meaning the opposite thing.

Sylvar was the first to find a clever solution:

"madam" (a respectable lady) is the opposite of "madam" (a brothelkeeper)
A related variation would be to find words whose exact reversal yields an approximately opposite meaning. A very weak example which springs to mind is "evil--live". broken-winged bird also came up with:
There's "on," which is the electronic equivalent of "yes," but if you reverse it, spells "no."

Email me (or node) further suggestions.