It means to chatter or babble pointlessly or at unnecessary length.
In that case I'd better be off, then...
Thing Not To Do Today: witter. This word arrived in English in the 1900s from a dialect word. It's very similar, and may be related, to the word twitter.
Twitter is much older (1300s), though it has recently begun to mean much the same thing as witter, except for the length thing.