An American friend has suggested that the term "rule of thumb" derives from an archaic English law forbidding a man from beating his wife with anything thicker than his thumb. I don't believe it either, but can't find a more persuasive origin. Any suggestions?

Geoff Cusick, Woking, UK

• Have a look at this URL: http://www.quinion.com/words/qa/qa-rul1.htm which has a long answer on this topic (and many others).

  Chris Stevenson, Bristol

• 'Rule of thumb' derives from the Miller's thumb. Millers in medieval times judged the fineness of the flour by rubbing it between finger and thumb to decide whether to re-grind it.

  Bill Kent,

• Brewer says: "A rough guess-work measure. Mesuring lengths by the thumb. In some places the heat required in brewing is determined by dipping the thumb into the vat." Morris gives a longer defintion, but it is essentially the same. Anyway, there is no eveidence of it being related to the beating law (did that ever exist) and has no obvious connexion in meaning. (I once read that French carpenters measured in something like inches until quite recently and that these were called "pouces" (thumbs).)

  B Rowe, London UK