From: utzoo!decvax!harpo!npoiv!alice!rabbit!ark
Newsgroups: net.nlang
Title: Re: words which mean their opposites
Article-I.D.: rabbit.1030
Posted: Fri Jan  7 11:21:46 1983
Received: Sat Jan  8 02:06:35 1983
References: dciem.137

This isn't quite in this category, but what about

	bimonthly

which means either every other month or twice a month, depending.