Here's an interesting, and a little archaic, use of the word "warn"--"to warn a" town meeting. It seems to be the only time when "warn" is used without a preposition and the object of the verb is the thing to which the warning pertains (that is to say, the object is not the person being warned). The Oxford English Dictionary lists the preposition-less use as obsolete, although it's found in one or two legal dictionaries.
It's a local term of art for announcing a town meeting according to legal notice requirements. The word is used in Maine, New Hampshire, Massachusetts, Vermont and Connecticut, and from statutes and legal cases it seems to tend to refer to announcements of special, rather than regularly held, meetings.