[thuhm] tumere (Latin) "to swell," tumidus "swollen;" (see thigh)
1. 1546 "All Thumbs": Awkward, clumsy; from saying, "When he should get aught, each finger is a thumb."
2. 1580s "To be under someone's thumb": to be completely under someone's control.
3. 1690s "Rule of thumb": An old wives' tale alleges that this term is based on an old English law permitting men to beat their wives with a stick no bigger than a thumb. Snopes has since debunked this claim: "The phrase is almost certainly an allusion to the fact that the first joint an adult thumb measures roughly one inch, literally a rule (or ruler) of thumb. "