Etymology
1. O.E.
þuma, from W.Gmc.
*thuman- (cf. O.Fris.
thuma, O.S., O.H.G.
thumo, Ger.
Daumen, Du.
duim "thumb," O.N.
þumall "thumb of a glove"), lit. "the stout or thick (finger)," from PIE
*tum- "swell" (cf. L.
tumere "to swell,"
tumidus "swollen;" Avestan
tuma "fat;" see thigh). For spelling with
-b (attested from c.1290), see limb. The verb meaning "to go through" (especially of printed material) is first found 1930, though the related sense of "soil or wear by handling" dates from 1644. Verb meaning "to hitchhike" is 1939, originally the thumb pointed in the direction one wished to travel.
Thumbnail sketch (1852) so called for its smallness. To be
under (someone's) thumb "be totally controlled by that person" is recorded from 1586.
Thumbs up (1887) and
thumbs down (1906) were said to be from expressions of approval or the opposite in ancient amphitheaters, especially gladiator shows, where the gesture decided whether a defeated combatant was spared or slain. But the Roman gesture was merely one of hiding the thumb in the hand or extending it. Perhaps the modern gesture is from the usual coachmen's way of greeting while the hands are occupied with the reins.
2. Derived from Middle English thombe, thoume, thoumbe (“thumb”), from Old English þūma (“thumb”), from Proto-West Germanic *þūmō (“thumb”), from Proto-Germanic *þūmô (“thumb”), from Proto-Indo-European *tūm- (“to grow”).
3. Cognate with West Frisian tomme (“thumb”), Dutch duim (“thumb”), Low German Duum (“thumb”), German Daumen (“thumb”), Danish, Norwegian Bokmål, and Norwegian Nynorsk tomme (“inch”), Norn tum (“thumb”), Swedish tumme (“thumb”), tum (“inch”), Russian дюйм (djujm, “inch”), Ancient Greek τύμβος (túmbos, “burial mound”). Also compare Welsh tyfu (“to grow”), Latin tumēre (“to swell”), Lithuanian tumėti (“to thicken, clot”), Avestan 𐬀𐬨𐬏𐬙 (amūt, “strong”), Sanskrit तुम्र (túmra, “strong, thick”). The parasitic ‐b has existed since the late 13th century. Doublet of tomb. See: German, old spelling '
Daumen', Swedish '
tumme', Welsh '
tyfu'.