The Collaborative International Dictionary
Thumb \Thumb\, n. [OE. thombe, thoumbe, [thorn]ume, AS. [thorn][=u]ma; akin to OFries. th[=u]ma, D. duim, G. daumen, OHG. d[=u]mo, Icel. [thorn]umall, Dan. tommelfinger, Sw. tumme, and perhaps to L. tumere to swell. [root]56. Cf. Thimble, Tumid.] The short, thick first digit of the human hand, differing from the other fingers in having but two phalanges; the pollex. See Pollex. Upon his thumb he had of gold a ring. --Chaucer. Thumb band, a twist of anything as thick as the thumb. --Mortimer. Thumb blue, indigo in the form of small balls or lumps, used by washerwomen to blue linen, and the like. Thumb latch, a door latch having a lever formed to be pressed by the thumb. Thumb mark.
The mark left by the impression of a thumb, as on the leaves of a book.
--Longfellow.-
The dark spot over each foot in finely bred black and tan terriers. Thumb nut, a nut for a screw, having wings to grasp between the thumb and fingers in turning it; also, a nut with a knurled rim for the same perpose. Thumb ring, a ring worn on the thumb. --Shak. Thumb stall.
A kind of thimble or ferrule of iron, or leather, for protecting the thumb in making sails, and in other work.
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(Mil.) A buckskin cushion worn on the thumb, and used to close the vent of a cannon while it is sponged, or loaded.
Under one's thumb, completely under one's power or influence; in a condition of subservience. [Colloq.]
Wikipedia
A thumb ring is a piece of equipment designed to protect the thumb during archery. This is a ring of leather, stone, horn, wood, ivory, metal, ceramics, plastic, or glass which fits over the end of the thumb, coming to rest at the outer edge of the outer joint. Typically a flat area extends from the ring to protect the pad of the thumb from the bowstring; this may be supplemented by a leather extension.
Usage examples of "thumb ring".
Since Mason cannot turn his head much to see, the index and middle fingers feel ahead like antennae as the thumb ring and little fingers scuttle the hand along.
Even if Obern had not known his father's hand, he would have recognized the broad thumb ring of High Chief, its red stone seeming to take fire from even that limited glow.